Our situation is probably a little different but we sponsored our nanny (who was already in the country) because her US husband does not have enough income and we liked her.
I would never do it again and will in fact withdraw sponsorship.
Things turned bad with her due to vacation scheduling problems (she wants 5 1/2 weeks, I suggested 3, she would not compromise). I mean, I have no leverage if I sponsor her. If I fire her, she can go on welfare and I have to pay for it. No.
I don't know how it is with work related visas though and how long you would be on the hook. Just remember, things can go from great too very bad really fast.