Chat bubbles create a community. Simple as that. The ability to talk to others standing around you, should be an enormous priority. There have also been times where chat bubbles have helped in pve boss fights as well. If a person becomes targeted for an attack, the game will warn players via chat bubbles, example : "flaming ball of death, on me!" This warns all players of the location and person the attack is going to be at. It would seem easy to implement. I'm not a game designer or developer, but just looking at it from an mmo player point of view, chat bubbles have been around for a while now, in multiple games and platforms, and it could only improve things.