Hello, I was wondering, when is the right time or the correct project size to start using project management applications ( like Redmine or Trac ).

I have a serious project, for now it's only me developing, but I use redmine to set my project versions, issues, and estimations. I think it's a good idea, because you never know when somebody else is going to join the team, and also allows me to organize myself effectively.

I ask this question because I was Teaching Assistant at my university for one year in a row for a course, and I got questions about this very very often. While I'm a believer of the KISS principle, I think that learning to use this tools early is a win-win most of the time.

I really believe that we can avoid this question to become argumentative, and that there's somewhat of a consensus about this issue, which I consider quite important in todays software development world.

So, when is the right time ? what is the correct project/team size ?