We use an IR camera to survey electrical gear for maintenance. A hot leg can tell you if there is a loose connection or corrosion. Also, an unusually hot component will indicate potential failure, like bearings. You can make a lot of money doing switchgear surveys for large power users.
They're also handy to tell where a roof leak is. Go in the attic after a storm and you will see a cool spot in the area of the leak. Great for early detection.