Trickplay and Chapter Images storage location.

[Nariagari]

This would also be possible if the trickplay is not stored in the config folder.
Jellyfin knows when a file chances, so it can delete the trickplay on rescan and generate a new one afterward. This probably is the current behavior anyway.

Also, if you delete a movie, you'd normally delete the folder and not just the movie file, especially if you store pictures and nfo files in the media location.

For movies yeah, since you generally store a single video file per movie folder (except for those with multiple versions of the same movie).

What I was referring to were situations where you simply edited a single episode in a season/show, or replaced a movie without clearing out the folder it's in.

I got what you mean.
True, Jellyscrub didn't delete those "leftovers". But I guess (depends on the code) that Jellyfin could delete these "leftovers" since it knew the checksum of the file and noticed that it changed. So it could delete the old .bif and create new a new one.

Or (in my opinion the better solution) the trick play has the same name as the media file, the same way .nfo files work.
It could be that the current naming is some naming standard, but it would make the relationship between files more obvious.
Also, if you replace a film/show, she files would be replaced.