Im sure it woulkd make you sweat more and like you said APPEAR slimmer, As for any actualy loss Im not sold and would say watch for dehydration.
For someone like a boxer/wrestler etc trying to makle weight It could be very usefull.
I know a female models etc. that use saran wrap and the like around the waist to shed weight. but these girls have eating disorders etc for the most part.
Maybe some others can chime in on the science side a bit more. All I can tell you is yes you would sweat more and the added heat would cause some expenditure of your body trying to cool itself.