I cannot imagine using git and having a reason to commit only half a file. I've known it was possible for several years. But never once has it been a solution to any problem I've had. I suppose we both have limited imaginations.
I know this is covering a mistake, but I've occasionally done one thing, then done a separate thing without committing (especially easy to do with things like one-line version bumps or super trivial bug fixes), then used git commit -p to commit+push the first change while still working on the second change locally. Obviously this only comes up because I suck at task management, but it is a real-life time when the feature is helpful.
