Not to forget subtitles.
If you rip discs, the subs are either in Vobsub or PGS format.
Both are picture-based and not many client types are able to render them atop the video.
Which then triggers transcoding.
If you seek better compatibility of subs with the majority of clients, you need to add in SRT versions of the subs. See Introduction: convert image-based subtitles to SRT with Subtitle Edit for one possible way to get perfectly synced SRT subs.