[xeonoex]

You can go by feel and sometimes appearance (and pretty much have to for some things like pork ribs), but the size and shape of large chunks of meat vary quite a bit, so does the weather, heat source, etc...

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.