Have you ever used git bisect?

Yup. A few times a year.

If so, how did you use it? Did it help you find a problem which would otherwise be difficult to find?

It helps me track down regressions, as in “this used to work, didn’t it?” or worse “haven’t I fixed this before?”.

I start a bisect, pick something relatively old, check if it works there, rinse, repeat.