Just be advised that it's not uncommon that when you join a duty in progress, the party might be dissolving and you end-up alone or when everyone is about to quit. If that happens, you will have no choice but to exit the dungeon (unless you're able to finish it all by yourself ) and you will have to start a new queue.

That risk is not much a hassle for tanks or even healers as they can queue faster, but as DPS it can be really annoying if you wait a long time then end up with a quitting party.