To understand whether it is worthwhile for you - we need to take a step back and understand what it is, and what it is not.
What is thermal imaging?
Using special infrared (heat-seeking) cameras, it can detect changes in temperature and display where it changes from hot to cold as a colored image. The main advantage of this is that it can quickly identify temperature differences and where these occur on a surface.
Thermal imaging was something previously only available to the military and in recent times, used in commercial applications.
How is it used for pre-purchase inspections?
The technology is slowly being adopted by the residential industry as equipment becomes more affordable to small operators. An inspector equipped with a thermal camera can use it to provide an indication on whether a house has insulation behind the walls. By scanning the external walls from inside the house, it can detect cold-air leaks and therefore indicate the ability of the wall to retain heat. A house with less cold-air leaks means it is more likely to have wall insulation.
An example of a thermal image is shown below.
Can it see through walls?
In short, no it cannot! This is a false misconception many people assume when seeing a thermal image. It can only detect surface temperatures HOWEVER when interpreted by an experienced operator, it can provide compelling evidence of insulation.