Precomps can make or break a project when it comes to organising. There are good ways to use them, and terrible ways to use them.
Our clients often ask us to reformat your videos (from square to portrait, for example) or supply a range of languages. Having a lot of badly labelled precomps spread out in different places in your project, makes the editing process very difficult for us.
If a precomp is essential, make sure you:
Name it appropriately (Animated_Logo is better than Precomp3)
Put it into the right folder (eg. Video 01 > Precomps)