A digital thermometer is extremely useful to measure the temperature of your ingredients, your dough, water, a baked loaf or even meats to see if they are cooked. It can switch from Celsius to Fahrenheit with an accuracy of 0.1 degrees and a max or min mode.
Sourdough enthusiasts can really benefit from a thermometer - ideal fermentation temperature to reduce an acidic taste (acetic acid especially) is 35 degrees C to favour lactic acid development over acetic which has a more pleasant yogurt like taste.
When mixing your dough you can measure the temperature of the ingredients and then adjust water temperature to achieve your Desired Dough Temperature - King Arthur Flour have a handy article on how to do this.
Similarly you can monitor room/dough temperature during bulk fermentation of the dough to control fermentation conditions. Or when you want to proof something like croissants where you shouldn't go above 28 degrees where butter melts and you lose those precious layers, but you want to get as close to 28 as possible to encourage fermentation.
Goes off too quick