My rule of thumb is that you can't expect people reading the code to go diving into the revision control history. So if a reader of the code needs the informati

My rule of thumb is that you can't expect people reading the code to go diving into the revision control history. So if a reader of the code needs the information, it goes in a comment. Commit messages justify the change; comments justify the code as it stands. I think these are different kinds of 'why' (though they can certainly often overlap a lot).