> They are still in the repo, but if no treeish item (eg. a branch) points to them, then they'll eventually get garbage collected.

Why else are you going to go through the trouble of rebasing master if this isn't the goal you're shooting for? I'm a big proponent of commit history hygiene but even I can't defend rebasing master except for egregious things.

I think the only time I rebased master except for this was to fix a poorly executed mass file rename that broke git annotate.