I'm only a little familiar when it was in aircraft, but it shortens the life of the motor as does most chemical injections, varied by the amount of use. Motors these days are designed to take long wear and over engineered, but only by a little bit. The extra pressure on the heads/valves will undoubtedly put more stress on the motor. But I would imagine if used only on occasion it could be fine.
It also generates additional heat and flash heat in the heads. Sometimes the rapid increase in heating can overcome the cooling and damage the valves. Again, the usual pitfalls of chemical performance injection.