I think if you have a solid system to work through and master ALL of the concepts in the core resources (UFAP), then extra information cannot hurt.
I think one of the reasons people tend to shy away from goliaths like the Robbins professional is that the information is just too much at times.
That is the issue that I have run into. I have a hard enough time mastering and remembering all of the little details that are presented in FA/Pathoma/Rx/UWorld that I could hardly conceive of the benefit of adding additional detail at this point. I am a big proponent of mastering core resources and coupling that with solid test taking strategy. It has worked well so far, and I am hoping that it works out well for STEP 1 in a few months.
Hypothetically, if someone masters UFAP as well as additional information then they are going to be even more prepared and would score higher on a given assessment.
However, if you are losing out on core information in order to pick up granular detail on other conditions, then you may end up at a disadvantage.