well, this may vary for others, but i imagine timecode is used in professional environments like i use it - specific reference points for editing. for example, if a client wants to edit their home movies, i create a 'review dvd' which has the timecode stamped right over the footage so as they watch, they pause, make note of the time and related changes on an editing form.. i hop on my computer and make the changes based on the timecode.
i have no idea wrt to the QT part of your question though.
Cheers,
Keebler