Many people read tarot perfectly well without utilizing astrological associations or (overt) numerology. If they confuse you, you don't have to use them until such time as a) you're interested or b) you have a better foundation with the tarot.
I would say their purpose is to help someone make connections if he or she is already familiar with one of those systems. The systems work fine all by themselves, and don't really need other systems to highlight them. Some creators, however, feel that synchronization is the way to go (and some authors have taken that tack generations ago). It's not necessary, though, so pursue it only if you want to.
