Adding my perspective from when Destiny launched this feature four or five months after the game's debut due to player demand. During that time, everyone began using PS Party chat outside the game.
When they finally launched in game chat, no one used it because the people who played together were in party chat, and wouldn't leave it to get on voice comm with randos.
And when we did join the chat for pvp with randos, they were idiots and jerks who didn't listen to strategy. So, not much different from not being on chat.