As others have said, it's a neat way to get content into your feed if you don't have something to write. You won't earn directly from it, but it could build you a following that could pay off later.
I've said before that I'd like a 'reblog with comment' to allow me to add some context to posts I share. If we could do that then I think there could be a split in the earnings, e.g. 10% to the sharer and the rest to the original author.
I think you get it ;)