I ask this because I have used a minuscule amount of Xanthan Gum to slightly thicken a chilli sauce I have made. However upon looking at the ingredients of many popular chilli sauces they all tend to use a "modified starch" (modified cornstarch, modified maize starch, modified tapioca starch, are the common ones I've come across) as a "thickener" and Xanthan Gun as an "emulsifier".   Given this what is the difference between a thickener and an emulsifier? How would my chilli sauce change if I used a modified starch instead of Xanthan gum? And why is it ideal to use both? 
Thermometers are really practical when you do not have a lot of experience cooking things; it let you keep track of the proper food temperature.  For example, I do not cook beef roasts often, so I will use a thermometer to not mess up my cooking and waste a good amount of money on a good cut of meat.  Thermometers are essential for confectioneries where exact temperature are needed, mostly for sugar caramel stages.  Thermometers are also essential if you decide to try "molecular" cooking techniques with different chemicals; where temperature needs to be precise for certain reaction to happen (I do not have examples for that). 