It's similar I suppose, but you'd have to be committing every 30 minutes or so (maybe your memory's better, but I find if you asked me to summarise what I did in the last 30 minutes I can fairly quickly; if you asked me to summarise my day, I'd forget half the stuff I did). And you'd have to be always working on the one code base (I've worked in places where you wouldn't have been doing that) or else you'd have entries scattered all over the place.

But yes, if you did those things, you could have that log in the commit logs, but it wouldn't be a fantastic resource - it's more useful to me to have that in a local file here, with just my entries (as opposed to having to extract my entries from the entire team's), in grep-able plaintext.

And you'd also be missing the notebook part of the picture; the stuff in there shouldn't be in commit logs (you're talking about notes from meetings, design notes, patent notes, paper notes, that sort of thing).