Infrared technology allows you to see different temperatures on surfaces such as walls, ceilings, and floors.  This can show areas that have missing insulation or moisture or hot spots in electrical panels.  The moisture from a roof leak on to a drywall will change the temperature compared to the rest of the drywall.  Even if it's been painted over and looks fresh.  A normal home inspection would not detect this unless going over every square in of the house (literally) with a moisture meter.  That is excessive and beyond the standards of practice for any home inspection.  What moisture meters are typically used for is to confirm suspect stains to see if a leak is still active based off the reading of the meter.  Infrared is NOT x-ray vision nor does it give off radiation like an x-ray.  It can't see into walls but it can tell a trained inspector a story of what might be going on behind the wall based off the different temperatures of the wall.