If you have a very good oil, high API rating, correct Viscosity Grades appropriate for your engine, there is no need for oil additives.
Motor Oils, specially the good ones are already loaded with many aditives to counter the effect of internal combustion.
It is equipped to handle even the most severe operating conditions engines will experience.
Low viscosity motor oils are energy conserving and ensures fuel efficiency. Some are designed for very low emission control.
However, if you have the extra money for it and will satisfy your curiousity, go ahead, no harm will bring to your engine(assuming its an authentic and good additive).