I don't use these things, so don't take my word for it, but my understanding is that the trigger price triggers the sale, but the limit price means that you will at least get that much for them if they sell. Example: You put in a stop loss at $1, and the shares gap down to 0.50. Without a limit price, you get 0.50 for your shares. With a 0.90 limit, say, then your shares don't sell till the price gets back up to 0.90.
