You can use the moves sent by friends in battle, but you can do that with guests (streetpass) as well. The unique thing that having friends lets you do is anilink - you can link one friends character to yours, so that they have all the Job levels and abilities that they do. I don't really use it since I kind of think it might make games too easy, but I still want to share my characters if anyone wants to The moves I do use sometimes, though.