Can facebook turn a bunch of garbage impressions into cash? Yes.
Can twitter turn a bunch of garbage impressions into cash? Yes.
Can snapchat turn a bunch of garbage impressions into cash?
Can twitter turn a bunch of garbage impressions into cash? Yes.
Can snapchat turn a bunch of garbage impressions into cash?
I wouldn't consider Facebook in the same group as Twitter/Snapchat.
Indeed, much of their expenses are for trying to grow as fast as possible, and cutting those could leave the potential for profit - but the entire premise of companies like this is that the potential earnings are unknown (but presumably high), thus they need to throw everything they have at it until they can find the kind of monetization they're looking for. I don't see it happening.