They're supposed to keep your grill clean, and keep your stuff from falling through. In the review it was just as messy, maybe even more messy, to clean the grill mat in the sink. Plus the one he used for meat never got all the way clean, even when he washed it in the sink and then put it in the dishwasher. It did great for the vegetables he cooked, tho.
You can also use these as baking mats, which seems like the better use. They're non-stick and you can cut them to the size you need. They'd be great for cookies, pizza, biscuits, or bread.