If it is a blood test ordered by your OBGYN then yes, it does much more. They check your iron levels, Rh factor, blood type, etc. All of which are needed to provide proper care for you and the baby. People seem to find it annoying to pee in a cup at every appointment too, but they're testing a lot more than hormone levels, like the amount of sugar in your urine, which could be an early indication of gestational diabetes. Just do what you're supposed to do and don't question your doctor's expertise.
A blood pregnancy test does nothing but test for hormone levels. So no, there's no point in having one done if you already know you're pregnant. Just see an obgyn for regular appts