How important is Facebook to a mobile game?

I think less important than ever. Facebook used to be the go-to place for free-to-play games with micro-transactions. Now it's all about iOS and Android. But still, developers give incentive for their players to connect their Facebook accounts. I think social network integration is important, but Facebook's popularity is waning with the younger crowd. I'd prefer a wider selection or for developers to provide their own social networks.