I have struggled with this question as well. I ultimately decided the fewer hours were a necessary evil. I came to the conclusion that making an A in every class was not optional. If it meant taking fewer hours (the fewest I ever took was 10), so be it. GPA, however, is not the weak part of my application. I used those semesters to beef up clinical experience and volunteer work which were severely lacking. If I am ever put on the spot, I don't think it will be difficult to make a case for this decision. On the other hand, overloading my self with classes and being forced to take some Bs may not even give me the chance to do the explaining. This is likely the rationale used by the councilor giving you the suggestion.
The previous poster has excellent advice - don't blindly take a max of 9 hours because someone has arbitrarily decided on this number. No one knows you better than you. Besides, if three of those hours are freshman biology or something similar - feel free to take more if you think you are able. I use that class as an example because it required far less time than general or organic chemistry.