The nice thing about this is that most objects, whether mechanical, electrical or fluid-based, exhibit some type of heat increase before failing. When electrical connections become dirty or corroded, they resist current, which creates heat. This heat increases the rate of corrosion, which increases the heat, until the circuit catches fire. In mechanical devices, lubrication, alignment and vibration problems create friction or require more power, both of which produce heat. Fluids also become hotter if their path is obstructed in any way.
Thermography can also detect failures in the insulating properties of materials.
If the seals on your home windows are failing, this will show up as heat around these areas. A common application is called refractory analysis. Over time, the bricks that line a furnace wear down. As they do, the walls get very hot. The earlier this heat can be detected, the earlier it can be dealt with.