It is a very positive thing to start doing.  Take the time to write down everything about your title when making a game.  You will not remember everything.  So having the, ever evolving, reference to look at, and code from, is a powerful thing.  It also gives you a chance to see if a new idea matches anything, and where it fits in the design.

Take it to heart, planning is a good thing.  Your project will not be done in 30 days, so plan for the long haul.  If you don’t you will be just like everyone else that never finishes anything.