The only thing that can really happen is that, due to the reduction in size, there's sometimes a bit of excess skin around the area that causes them to look a bit saggy initially, in the same way that losing weight around the stomach or thighs can cause excess skin to be left over - however, unless there is a huge size decrease, this skin will tighten up again in no time at all - the sagginess, if there even is any, will be gone within a month or so.
Hope it helps!