They are great for grilling, smoking poultry items, any kind of cooking where you need a quick reading of something to determine it's done. It lets you get in and out without losing much heat in whatever you are cooking with where an more traditional food thermometer might take up to a minute to give you a reading.
You'll find most of your BBQ meats like pork butt, ribs and brisket are better determined to be done by touch and feel, not by temps.
If you are looking for something to monitor smoker temps, check out the Tel-Tru line of thermometers.