I always keep a digital thermometer in my sleeve pocket at work and use it many times every single day. I believe because I do pastry, I use it far more than my savory counterparts. I always check the temperature of my ice cream bases, loaves of bread, chocolate while tempering and many other things. I have been cooking long enough to be able to judge when an anglaise reaches nappe, but have some recipes with other components that cause them to thicken early, yet are best when cooked to the full 180 degrees.
Added to that, we have a very strict health code here in Vegas, with the casinos all employing their own "health inspector" that monitors all of the food outlets to prevent problems before the "real" county health inspector comes. We use a blast chiller and need to log the temperature of every item inside, every hour and show that log to any inspector to prove we follow proper cooling techniques. It it quite the pain when the timer goes off during busy service-ugh! But we are all required to carry thermometers on us and show they are properly calibrated if asked.