Too many maps in one game can lead to lag, so it is best to keep them to a minimum. If you are absolutely sure you won't ever need the map again, you can delete them. But remember that players have a way of surprising you, and could one day say "Let's go back to that city we said we would never go back to!" As a Pro user, you have access to the Transmogrifier (<a href="https://wiki.roll20.net/Transmogrifier" rel="nofollow">https://wiki.roll20.net/Transmogrifier</a>) and you can copy maps between games. Many users keep a separate "Atlas" game containing old maps. With the Transmogrifier, you can keep your primary game lean with just a few maps for your current session, but can pull any old map back into play.