Some schools, like UCSF, have an honors/pass/fail system, where students vie for a hefty stash of H's to distinguish themselves from the pack. It was reiterated several times over the course of my interview day that the system fostered collaboration among students, but I can't vouch for that personally. With the boards going P/F, I'd venture a guess that, at strictly P/F schools, things like LoRs, externships, research, and outreach/ECs play a bigger role in standing out in the class. In response to the board's switch in grading, I think Case (any others?) moved their grading system from P/F, back to a traditional A/B/C/F format.