I'm that case (my Dropbox folder would almost fill up my hard drive, oh the joys of solid-state drives). You can either: a) use Selective Sync to only synchron

I'm that case (my Dropbox folder would almost fill up my hard drive, oh the joys of solid-state drives). You can either: a) use Selective Sync to only synchronise a few folders onto your computer, such as syncing the important documents folder but leaving the gigabytes of videos folder, or b) have Dropbox throw an error at you and stop downloading files when it runs out of room.