Code comments are best for spatially local concerns. Commit messages are best for temporally local concerns. Design decisions are temporally local concerns. "Wh

Code comments are best for spatially local concerns. Commit messages are best for temporally local concerns. Design decisions are temporally local concerns. "What if _" is something you just thought up today. Tomorrow you'll be concerned about other issues. A long code comment about something you don't care about will keep getting in the way.