Okay Destiny uses Peer 2 Peer to connect to it's servers, stupidly enough. This means that it is constantly using data when you are playing pve, pvp and strike missions. I found out the hard way by pure desperation I used the PPPOE option on my PS4 to dial into my Afrihost account because I kept getting the "Centipede" error code. It worked flawlessly, so my assumption is that Mweb was blocking p2p on my connection causing the login session to timeout all the time.
As for Data usage it is about 100Mb/s an Hour.