Hi,
You could move your artwork to get space on your drive, but I would suggest it would be easier to move your roms for specific systems to achieve the space you want. It's a simpler process. Although if you want to move art then you could, you would have to then relink your folder structure to the external drive. Best bet in that case would be use the same directory tree structure and change only the drive letter so there would be less to change in LB.
CHEERS B