Digital thermometers are a great tool when slow cooking meat.
It is pretty easy to under or overcook meat on the grill. Monitoring the internal temperature of your food, as you cook it, is a really good way to be sure that food is as done as you want it and no more. This affordable ThermoPen set-up does the trick for me.
I like to use one probe at the grate and one inside the item I am cooking. That way I know what is going on!