Downsides? Well, since you’re not questing, you can chew through your rested XP very quickly. Some of the old world dungeons are VERY long, and even experienced players can get lost easily. Because you’ll have new players, this means drama from any number of sources can spring up (everything is hunter gear again!). If the quest you want to complete in the dungeon isn’t directly related to killing the boss who gives the satchel, many groups will simply skip it. Finally, if you’re leveling any sort of gathering/crafting profession, your skills will stagnate (with the exception of skinning, which has good and bad instances).