Why organizing UV maps is important? What difference does a manually layed out UV make compared to an automatic one if I’m texturing my stuff in Substance Painter anyway? Many tutorials mention that you are “gonna have a bad time” if you don’t manage UV tiles manually, but I’m yet to run into any troubles for forgoing such advices.
Usually the layout isn’t much of an issue, I always use an automatic packer. The only reason to organize it in a particular way is if you need to understand it in something like Photoshop.
Sometimes it’s more convenient to texture in uvw projection. Imagine you have a clothes model in a particular pose, which is hard to texture with straight seams in viewport, but very easy when it’s unfolded.
Packing is important for games, where textures are loaded into video ram, and therefore add up quickly. For rendering it’s not as important, as clients always never even understand the process, and the output is image\sequence.