This is somewhat different from the parent's view, but personally, I try to turn the list of commits in a given PR into a readable, reviewable "story" of the general steps that need to taken to implement a feature or fix a bug. (This starts when first writing it, because splitting up changes after the fact is a nightmare.) However, I do not want to limit myself to finishing and polishing one step before proceeding to the next. For one thing, my intuition might turn out to be wrong and the overall approach I'm aiming for might not be a good idea at all, something which I might only figure out when trying to implement the final feature/fix on top of the foundations. Or it might be a good idea overall, but I might end up realizing later that, say, out of the code I was fixing up in a previous commit, a lot of it is going to be removed by a later step in the refactoring anyway, so I should probably merge those steps or otherwise shuffle up the order. For another, I will probably just end up making mistakes, some of which I'll notice myself and some of which may be noticed in code review; while the "story" is primarily for code review, it is also useful for bisecting, so even changes found in review are good to integrate into the story.

As a result, when working on the project I'm thinking of, I use git rebase -i constantly, as if each commit were a separate file and I were switching between them in my editor. However, I don't actually like that old versions of my code are being thrown away (aside from reflog); I'd prefer if Git had two axes of history, one 'logical' and one 'real' (even if that gives people who already don't like branchy histories nightmares). I hear that Mercurial has something like this called "changeset evolution", but I haven't tried it; wish someone would make a Git port.

>I reflexively ^S every couple of words...

Why not just decrease the autosave interval in your editor :)

>What's the purpose committing more often than logical chunks of code which can be considered in some sense "done"?

There are different degrees of "doneness". For example, (1) code that isn't finished but you don't want to lose it if the power goes out, (2) code that you're not sure if you're going to keep, but you'd like to be able to refer back to it even if you later decide to change it, (3) code that completely accomplishes its purpose in a logical and coherent manner.

I use "Ctrl-S" for (1), "git commit" to a local branch for (2), and "git rebase/git push" for (3). Maybe I'm just a sloppy programmer, but my workflow often involves writing some code, making certain changes, then realizing that what I really need is the previous version but with different changes. So for me, frequent commits on a local branch have replaced frequent saves under different filenames (foo.c, foo_old.c, foo_tried_it_this_way.c)

Can't speak for the GP, but I often commit my changes every 3-4 minutes with messages like "Tweaked the padding." Then when my work is in a reasonable state to be viewed by someone else, I'll turn those 5-6 local commits into one coherent "feature commit" like "Redesigned the page header according to new brand guidelines."