Hobby projects are a good thing. They give you an opportunity to do something different without the pressures of employment.
When you start involving other people in your endeavour, though, you’re turning it into something much more than a hobby project.
You could be building websites for friends, painting for an art show, volunteering with an organization – whatever.
As soon as other people are relying on you to do something, expectations are set, and your credibility+reputation is at stake.