Seems to work great for the local Dunkin Donuts where I live. You have to enter the parking lot to get the PokeStop, then you see their store, and are probably more likely yo come in and get a donut or coffee. I've grabbed more coffee from them since. It's basically like free advertising for them since people have to go walk by their store and actively think about going in or not vs. never entering the parking lot and maybe not noticing it. Sure the free advertising won't pull in every customer, but it will increase the average number of customers who come in.