If you've been cooking something a while, and the food temp you are reading on the probe seems suspect, it's nice to grab the Thermapen and do a quick double-check. Aside from the cost of whatever you are smoking, you can have a lot of time invested in a long smoke, and you may even be depending on the results (company coming over). You can do without extra probes and a Thermapen, but it's just a matter of time until you realize why most of us have these items.