Thermal imagery was created by the military to detect "warm bodies" in the dark. Like so much military technology there are many peace time uses for thermal imagery.
At SERVPRO, we use it to detect temperature changes within the walls and ceilings of a structure. If a portion of structural materials is damp it will present a different color signature and a temperature readout on the camera's screen. The benefit of using the thermal camera is the time it saves over having to use a hand held meter to press against various surfaces, and being able to aim it at ceiling and upper wall sections that would otherwise require someone to climb onto a ladder to make a reading with a hand held moisture meter device.