The preceptor is your supervisor/mentor while on rotation. No preceptor, no rotation. A lack of preceptors makes it hard to provide rotations to students, which is why having a large alumni base you can trust to guide you through the rotations properly can give the school flexibility in offering rotation sites. I know Western places you in a pharmacy in both your first and second semesters, I would imagine if they've got enough locations to put the class in P1 year, they probably have enough locations for P4, the difference will be the diversity. If they have 140 students and 90 preceptors in retail and 70 in some form of inpatient/hospital setting, you may not have certain specialties represented or probably more accurate, underrepresented (pediatrics, oncology, nuclear, psychiatric, organ transplantation, etc.) This means if you are interested in one of these fields you would probably have to do an internship to get experience if a rotation site is not available, and without a rotation in that area someone else's application for the internship would likely be more competitive than yours.