Ee0u, Viagra is not bad for you. If you do not have any contraindications or conditions that will make Viagra dangerous for you, it will be just fine.
Viagra can help you if you are a premature ejaculator and it shortens the refractory period dramatically, sometimes to the point where it only lasts a few seconds. So other than marathon sex and delayed ejaculation, it does not really do anything for a healthy man.
Take care!