Hi, NomadicBroos!
As I'm to understand subtitles, as opposed to captions, subtitles are supposed to be embedded into the video and called up when required by the designated button on a DVD(or blu-ray) player's remote control, otherwise they remain hidden. Captions, on the other hand, are on-screen info which, once the video is rendered, can't be removed, can only be "covered over". The subtitles, once embedded and the video rendered, also cannot be removed, but by design, they don't appear unless called up by the button on the remote control, thus there's no real need to remove them.
For myself, I tend to use captions to describe a scene when I can't be bothered putting in a narration track. Subtitles(like those on broadcast TV) are only called up to aid those with loss of hearing, the same idea is applied to DVDs and many feature movies contain embedded subtitles for that purpose, or, alternately to provide translation into another language other than English(or into English if the movie is spoken in another language). So there you have it!
Cheers!
Neil.