Even a car straight from the dealer should be clayed. On the back of a trailer, it picks up all kinds of impurities and dirt that you will miss by washing.
Claying is not something you need to do regularly, only before polishing and waxing/sealing a car. So you are probably looking at doing it every 3-6 months if your car needs a re-wax/seal. Did Liquid say they would use Gloss It or Zaino as a seal?