Why forgiving makes good sense?

If someone has done grave injustice to us, we keep fuming over it. We carry a grudge against him. we keep on carrying it on our mind. what is the fallout?
a) Physiologically speaking, our BP goes up and causes damage to our health system
b) Spiritually speaking it starts a new Karmic cycle

Hence it makes good sense to forget and forgive ..... and be happy today and move to eternal bliss of liberation from the cycle of birth - death - birth - death ........ eventually.