Actually, there’s more to low-poly than just cartoony stuff. In fact, there is a common misconception that low-poly = more cartoony. Technically, low-poly literally just means a lower poly count, and should not be used to describe the minimalistic art style most people in this thread are describing.
Low poly building is a great way to reduce the amount of memory your game uses since it has less triangles than a more detailed build might. This means that using such a building style for your game will be much less costly than using the same style for everything. This has been practiced for years in many, many games inside and outside of Roblox.
Generally, low-poly objects are used to create small “props” in the game that need to be duplicated over-and-over again. With techniques such as instancing, this becomes very viable since they only have to be drawn once. However, it’s also great practice to use it on larger objects such as terrain too, since there doesn’t need to be too much detail with such elements.
Low poly house props. These would be used multiple times throughout the game.
Low-poly windmill. Keep in mind that it looks realistic, but is still technically low-poly.
On Roblox, 100% of the meshes uploaded are also considered low-poly since they are limited at 5,000 triangles (or is it 3,000? Oh well, you get the point.) This does not mean they have to look minimalistic, and many devs have used such low-poly meshes to create super realistic things:
So basically, low-poly =/= minimalistic building style. It’s actually just how many polygons are in a certain model, place, etc. When somebody mentions it, now you know that they might be talking about something totally different.