It entices customers to checkout by displaying a coupon code. We investigated the uptake rate and it is linked to the fact that customers who use the "back button" in the browser window to shop will also see the offer. So they may not be leaving your store, just returning to the previous page but now you have shown them how to get your products cheaper.
This app does not track sales made from people taking the exit offer. I may cancel before the 14 day trial is over.