I have always one or several projects running, it’s fun and educational. Someone once said: 

-"You dont learn to write well by writing many things badly, but trying to write few things well."

This is also true for developers. At work we are influenced by bad culture, bad habits, time limits, stressful workplace (bad environment) and other things that makes it hard to produce high quality applications. When you are met with a challenge you need to train for the specific task. 

But projects can also be fun and educational in other ways like exploring areas you never have tried before or just to still your curiosity, many times when my curiosity is fullfilled the project dies. And here are some of them 🙂

This is my old hobby room – when it was a huge mess (to many projects at once)