At a previous job, with a huge C++ codebase and ~100 developers over 20 years, many platforms supported, a build could take hours, and the test suite took so long to run that it would take several days or weeks of real time to get through it all.

This cycle time combined with occasional unexpected interactions between components meant that in every release cycle, there were dozens of complicated failing tests where it was not obvious which code change was responsible.

`bisect` here was extremely helpful: instead of having to pore over commit history and think very hard, I could bisect with a small wrapper script that would build and run the failing test in question. Builds still took hours, but I could usually autonatically pinpoint the responsible code change for one of the tests overnight.

(This was not using Git, but Perforce, for which I had to write `p4-bisect`. Alas, it's not open-source...)