Oh, this is not to take the place of tips! We've done this in hotels around the world and when we tell the maid that we're leaving clothes in the room that we don't want (don't mail them to us!), so many are just tickled.
I'm not sure stewards on ships feel the same way. We want the extra room in our suitcases and if leaving the clothes are problematic, we will just toss them before we leave the ship. I thought I'd ask a crew member so we know