I'd have thought shedding some weight in a race would be quite welcome! I'd be interested to hear how one would extract the "weight" from ones tight cycling shorts whilst going full gas though.
Personally I've never been caught short, not for a number two anyway, I'm as regular as clockwork on that front and won't even go out on the bike if "my time" is close. I'll wait till I've done the deed and then go out.