Many material frequencies, especially for explosive compositions, lie within the THz spectrum.
In addition, THz waves have low photon energies—one million times weaker than x-rays—and will not cause harmful photoionization in biological tissues. In standard English, THz frequencies are fundamentally 'bio friendly'...meaning they're non-hazardous and will not sterilize men, cause dogs to twitch, force birds to crash & burn from the sky or, sad to say, heat your Meals Ready to Eat (MREs). THz, thus, provides a significant advantage for both imaging biological materials and in operational contexts where an operator or other subjects may be exposed to THz radiation.
THz can also penetrate or pass through a number of commonly used materials consequently allowing one to identify what's inside or underneath. This characteristic enhances THz's ability to be used in non-invasive and non-destructive inspections.