what is the new LFD function I assume they have changed the join a party thingymijig where you used to put yourself in queues in LFG?
laters elv
You say to it, "Give me a random heroic", set your role or roles, and it assembles a group for you from people in your battlegroup and teleports you to just inside the instance. Tank queue times are almost nil, healer queue times can be as much as five minutes on a slow day, dps is usually about ten minutes, which you can spend doing dailies or gasbagging in gchat. If someone leaves partway through, a replacement is teleported to your location rather than the beginning of the instance.
You can pick specific instances as well, but if you pick a random it gives you the two extra badges or, below 70, a bag of useful goods that I believe contains a blue item of about your level you may or may not be able to use. I don't know, I've never used the completely random dungeon tool below 70 because there's always an instance within range that I don't want to do, like Gnomeregan.
You can vote to kick bad players, but only after fifteen minutes. If you abandon a group you get a deserter debuff and can't queue for another random. I think it's 30 minutes from the start of the instance, but it's changed a few times so I'm not sure.
Battlegrounds recently got some similar functionality. You get honour bonuses for using the tool and a huge amount of honour for your first victory in a random BG. I don't use it much though. Five years of watching the same mistakes being made in Arathi Basin have kind of left me a bit over it, feral druids don't do well and nobody guards you when you're healing.
You get all sorts of groups in random dungeons. We moan about the bad ones but you can also find yourself in a group of solidly competent players who so hugely over-gear the instance that they go through it almost without stopping. Mobs die in seconds, the tank is so sure he's got aggro he doesn't even wait for them all to die before running towards the next group, no one ever stops to drink because everyone's talents and gear are constantly regenerating more mana than you use and you get the whole thing done before the vote to kick time limit is reached.
