Atomic commits compose easier. In case you want to pull a few out to ship as their own topic. Or separate out the noisy changes so rebases are quicker. Separate out the machine-generated commit so you can drop it and regenerate it on top of whatever.

My commit messages are pretty basic “verbed foo” notes to myself, and I’m going to squash merge them to mainline anyway. The atomic commits, sometimes aided by git add -p, are to keep me nimble in an active codebase.