Maybe I'm an idiot and don't understand the marketing lingo but what exactly is the use-case for this? Why among all of the tech companies is Facebook the one to create a crypto currency?
I think the idea is you're going to be able to "Message" other people "money", Straight from the Facebook app/website. It also should work seamlessly across the various other social networks that are partnering in this.
There are other ways to do this now, but if they are able to do it right, this would generally be more convenient and widely available. I would assume fees will be low to start with. (Note that Visa and Mastercard are partners, so you can safely bet the fees will go up quite a bit once this catches on.)
What do they plan on doing with this?