Have you ever tried to watch a video with the rotation lock enabled? If you want to watch that video in landscape, it can make for a frustrating experience.
It means having to open Control Center, disabling rotation lock, and then rotating your device so that the video goes into landscape mode. And then, when you’re finished with the video, you have to re-enable the rotation lock if you want it back on.
Instead of going through all of that rigamarole, wouldn’t it be better if iOS took care of all of that for you on the fly? It will, if you have AutoRotateVideos installed—a new jailbreak tweak that can make watching videos on your iPhone a more pleasant experience.