As on YouTube, it would be nice to be able to jump 10 seconds back with the "left arrow key", and 10 seconds forward with the "right arrow key".
Use case 1:
When watching a movie, it happens that you are not quite sure what they were saying, you can easily skip back to the scene with one easy-to-remember press of the "left arrow key".
Use case2:
The movie has a boring scene, you can skip it easily without going too far with pressing the "right arrow key" multiple times. If you jumped too far ahead, no problem, just press the "back arrow key".
Comment:
Honestly, I was very surprised that this was not implemented already.