My question is does this cause my mt-daapd database to become bloated when they are moved or does it also remove entries when files go missing?
It removes stuff from the database, and every startup the server does a “vacuum”, which reclaims space from the database, so the database gets shrunk every startup.
On a side note (but I think this is related) what is the difference in the web interface between “start scan” and “start full scan”
A regular scan just kicks off a regular incremental scan — one that looks for files that have been changed and updates the database for changed files.
A full scan empties the database and builds it from scratch, so that it re-imports data from every song.