When a change is "trivially small" (a rarity), leaving just a commit title without additional detail works just as well of course. Adding the extra detail on somewhat larger commits helps me understand what I just did by recapping, and may also help another developer spelunking in the commit history someday. In terms of productivity I don't find myself spending a great deal of time on it...it's just jotting notes :)
Too mutch shuffling between different attempts could lead to difficulty in navigation the different attempts.
I reference vim because, like emacs, it has undo trees. Vim has a decent concept of an edit. If I extrapolate vims edits to commits I would find the history to be invaluable.
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