Proximity chat should always be turned on, and you can't be heard unless you are within extreme close range like 1 or 2 meters away. Since there will be no matchmaking for raids in Destiny then proximity chat is the next best thing, be able talk to people in the tower outside your fire team to get more to join up would be a good thing, as well as in open world maps you can warn others when they are in danger, since explore maps can be entered solo, having a proximity chat would be an asset. It would be even better for pvp because i love being able trash talk with people i kill or get killed by that's in close range