It is a quicker way to defrost. I will defrost in a zip lock bag in a bowl of hot water, only if I forget to take it out of the freezer in the morning. But I find defrosting without the water over the day is better, that you're guaranteed to drefrost the whole rat/mouse completely with no cold spots.
I usually run the rat under water just to add temp to the body, but also a way of getting snake to drink water without them knowing.
I like using the zip lock bags for hygene reasons because my fiance is not keen having rats lying around the house. I spose loose rats/mice in bowls or tubs of water is ok for some people. Not aloud in our household.