Excuse my complete ignorance but how does measuring the temperature of food help you with cooking? When I do a BBQ, I've only ever judged by colour and appearance. Usually the challenge is not to burn the outside while the inside is undercooked.
People did make good BBQ for many years before digital thermometers existed, and without using meat thermometers! I suspect professional experts barbequing all day probably still don't use thermometers. They are have the same heat source many times, and know how it cooks and know how to judge the size of meat, because they've done it hundreds of times.
But yeah, for those of us who are less expert, a meat thermometer can get us much better results.
But a thermometer let's you transfer those skills much more easily to environments with varying conditions, It's especially common for professional cooks to be expected to cook in varying conditions.
If you're a restaurant that is constantly smoking meat, you probably don't need a thermometer, but you probably have one. If you're an ordinary person, I would recommend a decent one at least. I have a thermapen. I don't regret buying it. If my fire dies and I don't feel like chopping more wood, or if I just put the brisket in the oven to finish overnight after it gets smoke, I can still know exactly when it's ready. I don't have to repeat the exact same process every time for a good result.
It has to be a repeatable processes, especially if you are doing it commercially and you need to train other people. Temperature is a measurable thing vs look or feel which is subjective.
For some things accuracy is extra important, one or two degrees won't make or break a pork but but can greatly impact something like steak.