I addition to getting rooms not otherwise available, I actually have been able to get substantial discounts at convention rates. Often as much as a 50% discount. However, this is more likely to happen for smaller shows that are actually held within the hotel. You can find them in the Tradeshow Week Data Book or online.

Obviously for big shows that place a heavy demand on the entire city, there will be very little convention discount. For some, like COMDEX, getting a room at any price is a good deal.