Hmm, I just tried enabling the left/right attack in training mode.
What happens when the left attack mode is enabled is that all the players shift slightly to the left. Vice versa for the right.
What's interesting is that when both are enable, the left move rightwards and the right move leftwards. Meaning it's more central like. The RB and LB are more central.
But i do however notice that they are more attacking minded and do drift to the edge during normal play.
But still, they don't storm/overlap forward when there's a clear running chance.