I'm trying to start playing in the pre-made worlds with the pre-made sims with all EPs installed, so I want to have a complete experience in every single world. Community lots are an essential part for this, but unfortunately the worlds can't have every single type of lot in them: either for lack of space (in Sunset Valley, for example) or because one kind of lot assignment doesn't really add anything that other lot assignment add.
With this post I'd like to comment on how neccessary I think each lot assigment is, and I'd like to hear your opinions. So this post is partly a request for some suggestions on what's "the best thing to do", but also as a resource for those interested and to share what you personally do in your games (make your own lots? use the default lots? add them when you start to need them? It really depends on your playstyle).

Base game

They are included in every world, so nothing to comment here. In older worlds it could help replacing the default rabbitholes with multi-purpose rabbitholes (such as Hospital+Lab), but I personally don't want to do that because I don't really want to remove/replace lots, just add.

World Adventures

• I don't really know the details about this kind of lot, but Market can be an interesting lot assignment to make mall-type lots with different registers (from WA and other expansions and the Store). Not really an essential lot, but interesting to add at certain point if it correctly works, or to save space by combining different shops in one lot.
• Nectary isn't really needed as every world has access to France. But nectar is a cool feature to have, so building one at some point can be interesting.
• Academy, unlike Nectary, doesn't seem fitting for most worlds. I'd leave them to China only. Same for Chinese garden (just a park that gives a special moodlet).

Ambitions

• Consignment store, Fire station, Salon and Junkyard are automatically placed on every new save for a reason, as they introduce many basic features from this EP. The only problem is where the game places them in most worlds and that they didn't include a variety of lots, so they have to be built or (what I do) downloaded from other players.
• Laundromat isn't essential, but to get the most of the laundry system there should be one.
• Hangout doesn't really have a purpose (that I can think of) with the lot types that other EPs added.

Late Night

• This is a bit complicated, since there are 9 types of lots and in the end maybe only having one type of Bar, Lounge and Club is enough to start. Of them all, Dive Bar, Dance Club and whatever kind of Lounge are the most useful as they allow the Showtime careers gigs if a scenario is added.
• Film studio is needed for the Film career. The rabbit hole is big, but at least creating a lot for it doesn't really require much effort.

Pets

• Equestrian center is another required lot for basic features. Thankfully, like the Film studio rabbit hole, they are easy to build. The small default version is good enough (its default placement in most worlds is the main problem, but that can be easily fixed in Edit Town).
• Pet store is a cool open shop to have.
• Dog park and Cat jungle are just special parks that attracts those animals, I guess. I don't think they are essential. Horse ranch seems the most useful of these lots, as a community place to learn horse skills. Still only needed when there are playable horses, I guess, for those that have horses in their houses but not a big yard.

Showtime

• Since other lots can be used like these if they have a scenario, there is flexibility whether to add a Coffeehouse, Live show venue and Private venue. What they do is essential to get the most of this EP, and the game acknowledges this by adding them to any newly created world (again, they are copies of Starlight Shores' venues from the lot bin and their placement is awful). To save space, the best idea is to add the scenarios to compatible lots that allow the specific gig types (like I mentioned in the Late Night section, but there are more possibilities).
• Adding a scenario to a park is also required for gigs (the game also places a park with a stage from the lot bin).
• The Big show venue is also cool to have for the highest level gigs, but it's not essential. It's a very big rabbit hole that doesn't look good or fit most worlds. But to get the most from this EP this is needed, so... I've read that, as long as the lot is assigned as Big show venue and has a stage it doesn't matter if the rabbit hole shell is added. I have yet to confirm it.

Supernatural

• The rabbit hole Arboretum, Vault of Antiquity and Gypsy wagon are also essential for many basic features. They are small rabbit holes, so they don't really need a new lot, they can be inegrated on existing lots in most worlds.
• Elixir consignment store is another useful shop to have.
• Supernatural hangout is useful if there are enough supernaturals living in town. I guess it's special enough to be worth having besides the LN venues.

Seasons

Thankfully, EA created Festival grounds for every world and they made it so they are automatically placed in new saves. Saves a lot of work.

University Life

• Arcade, Nerd shop and Rebel hangout are interesting on their own and also as lots that attract the specific social group sims. I'd add them to the worlds.
• Java hut is very useful as a non-rabbit hole café. If this lot assignment can be used as a Showtime Coffeehouse venue (I'm not sure, can someone confirm?), then it can be a good replacement for the Flying V's rabbit hole Coffeehouse (that's just a bistro with a stage). With the bakery Store content this lot assignment gains even more relevance.
• Student union, University hangout and the university rabbit holes don't seem useful outside the university sub-neighborhood, even if they are allowed in the home world.

Island Paradise

• Resorts are good for every world. Even if you don't own them, I think they are cool to have. Better with the rugs mod to not need the rabbit hole towers, I guess. Definitely I'd add more than one resort to each world.
• Diving areas are needed for the scuba diving skill, but the problem is that most worlds don't have space for them. I've read that, of the non-store worlds, Sunset Valley is probably the only one with space for them (besides Isla Paradiso, of course).
• Ports are needed for houseboats, but again most worlds don't have enough sea space for them. I'll see where I can add them (only one per world). Definitely Riverview, Twinbrook, Bridgeport and Appaloosa Plains aren't places for them (either for the space or thematically).
• The Lifeguard chair is not a lot, but is worth mentioning here as an item that needs to be manually added to each beach in every world in order to have access to the Lifeguard profession (I also have a mod installed to allow this profession on pools, so I add them there too).

Into the Future

• Business park, Dried up beach, Wasteland and Future lounge only make sense in Oasis Landing, I think. If anything, in Lunar Lakes from the Store.
• Bot emporium isn't really needed in the home world and can also break the immersion.
• Cafeteria could have its uses. But then again, we already have Hangouts, Coffeehouses and Java huts to make a place to drink coffee / eat...
• Gallery shop as a clothes store can be interesting to have. I don't know the details of this lot, though (if it's like TS2's clothes shops or limited to futuristic clothes).
• The Plumbot competition arena and Stellar observatory add careers and skill classes, but the rabbit holes aren't really fitting for any world outside Oasis Landing. I think there are rabbit hole rugs for these as well, but I need to look further into these careers to know if they properly work as "normal" jobs in the present timeline.

The Store

• None of this is essential, but I wanted to mention it anyway as there are premium items that allow some interesting places that may be worth adding to some worlds. For example: casinos, open restaurants, any kind of shop, open spas, bakeries, sport centers, the skydiving center rabbit hole... And some other items can be added to existing lots, such as public showers, dance floors, ballet barres, wave stations...