When you say credits, do you mean the 35 contact hours of training? If so, the reason PMI has that is that there are a lot of "accidental" PMs out there who have never had any formal PM education and they want to ensure that before someone sits for the exam they have a solid grounding in the fundamentals.
Anyway, it is better to review the whole concept of PM in a very structured way. It helps you to form your understanding and summarize your experience. Saving Changes...