Annual health check-up is a method of complete body examination. The tests that are run to help in detecting if there is some kind of virus or bacteria or any other problem festering inside your body. Early detection leads to early treatment and also increases your chances of being cured.
Getting your check-up, tests, screenings and diagnosis done before anything serious happens is the best way you can deal with any disease. In the case of venereal diseases or diseases like cancer proper diagnosis is required so that it could be prevented, cured or avoided altogether.