I'm pursuing my PMP certification, and while I have many years of PM experience, I have only just started my 35 contact hours of training for the PMP. At the beginning of that course, the instructor mentioned that if I join PMI that PMP practice exams are available as part of my membership.
It occurred to me that I could take a PMP practice exam as a "pre-assessment," which would help me to know what areas I need the most study. However, I'm not sure if there are disadvantages to this approach, e.g., that PMI only provides a single practice exam, one I would like to "save" for when I'm done studying so I can judge my ability to proceed to the real exam (if I had already taken it, I couldn't re-take and make use of the results, since I'd have seen the answers on my prior exam attempt).