We primarily use our instant read therms in the kitchen (I bought one kind and bought another kind for my wife) and we swear by them. Takes all the guesswork out of if the food's done or not. But I noticed that with ground meats, some roasts, and whole chickens/turkeys the temp can drop when you insert the probe in a particular area. It could be that the meat is cooler in that spot than in another one, or perhaps the meat isn't as compacted as in another spot so the therm is being inserted into a gap, causing the temp reading to fall. I've seen this happen many times; when it does I just search for a spot to reinsert the probe where it gets an accurate reading and I always find one.
Here's the importance of a good instant read thermocouple therm: For Christmas dinner I cooked a boneless ribeye roast, using a single probe therm that I used to use for my smoker. I was looking for an IT of 125° so I could pull the roast out and the carryover would take it up to 135° (according to the recipe). The therm showed 125° but when I checked it with my CDN knockoff of a ThermoWorks Thermapen (I've already calibrated the CDN) the IT was at 135°--a whole 10 degrees warmer. I took the roast out of the oven and let it rest. After making the first knife cut I saw that it had been cooked perfectly--I lucked out. But had I trusted the first therm, which was a Taylor under the Food Network nameplate, the roast would have been overcooked.
I also have a Maverick Laser Surface Read Therm Gun to check the temp inside my Weber charcoal grill and inside our kitchen oven. You don't need that but you should consider an instant read therm. I bought my wife a ThermoWorks ThermoPop for $25--but you can find them on sale sometimes. Their Thermapens are extremely popular but you can buy cheaper knockoffs made by CDN, Thermowand, and others. Only ThermoWorks manufactures their therms in England; all the others are made in China. I really like my CDN and my wife loves her purple ThermoPop.