Official comment
If you have moved from:
user/Music Collection/..
to:
user/Dropbox/Music Collection/..
You've already done the "parent" folder and the mass-relocate will find all content within simply by relocating the first song.
If you are moving files in a more specific structure, as you note in the second example, it's better to relocate them if you don't have many tracks where you've had to edit the beat grid, add custom memory / hot cue points. If they're only in the collection in a very "vanilla" way, you would be best off removing them from the collection and re-importing.

