Typically you would atlas a UV because one great way to optimize game assets is to have as many assets as possible all using one texture map and thus one material. For example, let's say you have several models: a ketchup, mustard, relish, salt, pepper, plate, fork. You could give them each their own material, but these objects are small and could all occupy space on one big texture. In the game engine, this means only one texture being sampled and often batching them together, fewer draw calls, and so on. Things like this allow major speedups. It's not always possible to atlas things though. Large objects demand their own space if only to maintain texel density as desired. For decals, especially small decals, you should always atlas them for the same exact reasons.

There's also texture arrays, where you have an array of equally sized textures in the shader, and then for each vertex you need to store an index, which is the index of the texture that the face is using. Probably some pros and cons to consider there.

@@SkeleTonHammer Can you pls give me a good article, or video .. about uv atlas? Im hearing this first time