Lichess is great for this indeed. Because you can 'only' put 64 games in I decided to create a new study for each year. Which helps to bring a bit of order in my chaos.
Not a bad idea, and if you play more than 64 games each year, you can just divide your studies into half/quarter years for instance. I think I will re-arrange my studies too, I have done it per tournament, but it gets pretty messy
It's strategic and tactical training of what actually happens in your games. You'll also have more insight into your thinking process, and where your mistakes happen. Chesscom or other apps won't tell you "here you were short on calculating", "here you didn't think of alternative moves" and so on
The analysis improves your thinking about the game and helps you understand what you need to do differently. Annotations encourage you to take more care and can also be useful for you to review. In the Dojo, you're also asked to publish annotated games, which according to Jesse has led to high quality work by students.