Not very often, aside from maybe using git blame to ask someone a question if I'm touching something they worked on recently.
Yet I've used git bisect to track down difficult bugs, which is dependent on that history. Not often, so I think of the full history as akin to a seatbelt - you might only need it rarely but when you need it, you really do need it.
I sometimes browse the commit history for a project, but it's more useful when scoped to a specific file. In addition, I use git blame, which depends on the commit history, quite often to understand the reason for a code change and the author.