I was required to present my Loews First card at check in during my stay at the PBH last year. However, I suspect they have access to a Loews database which ought to be sufficient to secure your name and sign up date. They did not inquire about my amenity preference, so I made sure to make my request for cookies and milk at check in.(They were delicious)
Loews First gives you frequent flyer miles, free room upgrades when available, complentary access to resort work out facilities, a morning news paper, and an amenity as annieecho describes.
They also send mailings to entice you to one of their many resorts around the country. They all look quite spectacular.