If you use TDD and a good IDE, you don't need atomic commits--every test run stores the state of that file to its local history. That keeps the commit history clean and uncluttered so if you're looking for "why is this code like this" you don't have to look through 198 insignificant commits. Also if you have someone on your teem who is responsible for the change logs, it makes it easier for them to see the actual changes that need to be included.