Like many others, I do a little coding in my spare time and use a revision control system to track both my development and changes. The amount of spare time I have available varies greatly from week to week and month to month. Many have been the occasions when I would not have any time to code on a project for weeks or even months on end, and such time as I had would typically range from 10 minutes (typical day) to 40 minutes (good day). Those certainly not great conditions--especially for debugging problems.

It was essential to keep notes that would both not get lost, and were easily retrievable. At the end of each session, the session's work would be committed with a detailed message. I could then go through the commit history and track my progress and thought process. This allowed me to pick up where I was last week, or last month with the least amount of precious time lost.

The point that I am trying to illustrate is that good commit messages help you (and anyone else who comes after you) to figure out what has happenned, what has been going on, where things are going and above all else why.