I really live having good formatting and spell check in the commit messages. It's much nicer than the `git commit -m "blah"` messages. Sure I could use another GUI, but magit is very easy when I'm already in emacs.
If you give developers a "lazy" option, a lot will default to it, which isn't ideal. -m is an alternative for a quick commit and end up being front and center when using the CLI.
I have flyspell-mode enabled for git-commit-mode. Avoids embarrassing typos in my git commit log.
It's little stuff like this adding up, making Emacs too great to ever be without.