Back when I used to autocross, the ideal PSI was a tradeoff between response and traction. For max traction we'd run the lowest pressure that would not allow the sidewalls to roll over (checking tire edges after each run). This was on DOT legal R tires and we were cornering at > 1 g lateral. But that low pressure can make the response a bit squishy so you might want a few PSI higher. Either way, we usually ended up running lower pressures than OEM recommended. Due to the tight courses, we weren't going much faster than 60-70 mph peak speeds, so we could get away with lower pressures than you'd run at higher speeds (like around a track).... And last, sometimes the inflation spec is for handling reasons. I don't think you can know if that is the case without going through the math.
Some people replace tires with something a bit bigger and wider than OEM, in which case you may want lower pressures.