I have to say that format-patch and am workflow is really handy, even when working alone. (Say you want to test a commit on multiple dev machines but you're not sure if you're ready to push to a remote, as an example.) The flexibility to store or transmit a commit in patch form apart from .git or the remote, then seamlessly add it to the history, is a good thing.

> Obviously you have to use a command line mail client too

Not really. You could use a GUI client like Thunderbird to respond to emails pertaining to a particular commit as long as you're not actually trying to paste code in the composer. If you want to put something like a code snippet delimited by a "scissors line", then you'll need to use git format-patch and/or git send-email.

In other words, it doesn't matter what MUA (Mail User Agent) you use if you're just sending text, but if you are sending code in the form of a diff that someone will apply using git am, then you'll have to use a tool like git format-patch and git send-email to compose the message and send it.