I think you mean such a use case:

1. The video is very long (e.g. 1.5h)
2. You watch some part and save video (title, url and time are automatically filled for YT)
3. You come back and watch from the last saved point
4. You must stop video for some reason and save it again, delete previous saved video

I think it can be a little bit annoying and I think I would add something like video tracking/video watching option or something like that. And I think this would solve this problem (the video will be played from last played position).

If you mean something else, please describe your use case :)