Do you really think they're implementing it for PLAYERS' benefit? Seriously? It's just a social hook to motivate people to talk to their friends about it and try to get other friends to play it. Pyramid scheme crap. I've never seen a friend system in any mobile title that's really about having a friend list, rather than it being an excuse to get people to spam their friends and promote the game.
A respectable mobile game like TERRA BATTLE does it in a much more graceful way. You are asked to refer friends directly, and you get rewards for each referral. But there is no friend list. If you want to play Co-op or PvP with friends, you can create private rooms and share the room code directly. It's great.