I’m more of an ‘All Welcome’ sort of a person.
So I can only comment from that perspective.
On the Plus side; Newbies seem genuinely eager to learn, I have no problems controlling the pace of the dungeon, and most people that join seem to have read the LFG description. On the whole people seem in good form on an execution level; they may not always know what to dodge, but actually doing it they manage well.
On the negative side; Less consumable use, and I have to do alot more wrangling to preserve the ‘no exploit’ clause I make my groups with. On the whole folks seem to have less fight knowledge and less grasp of structural mechanics (ex; combo fields).