If you are looking for a PGY-1 residency, the PPS would not be a good use of your time and money. All the residency programs will be represented at the Residency Showcase, the purpose of which is to introduce the programs to the potential applicants. The purpose of the PPS, on the other hand, is to provide a venue for people interested in interviewing on-site with participating programs. For a fellowship seekers it is a must, for a job seeker it may or may not be productive, and for a residency seeker generally not worth the investment.
What I would suggest, is NOT registering now, and waiting until you get there. Get your hands onto the booklet, and if you are interested in specific programs (especially after the showcase) and you see that they are interviewing at PPS, then you can register onsite.