The two picture show bathroom venting (left) and a bathroom fan (right) ending in the attic.  Both are bad because they will put moister in the attic and cause mold.

                    
You never know what could be living in your walls.   It could be a small as termites (left) or as big as a raccoon (right).

                    
Rusted ducts (left) and appliances, such as water heaters (right), can be hiding anywhere.  Finding them as soon as possible can help save you hundreds of dollars.

                     
Thermal imaging help to show where heat lose not visible to the naked eye occurs.