you want your presures to depend on how you ride/if theres a pillion.
like XROWDAC said, if you do a LOT of curves you want to drop your pressures slightly for a greater contact patch for grip.
if you commute a lot in straight line. then you want higher tire pressures.
Example: my road bike runs 44 psi rear and 38 psi front. ( a fair bit of straight line riding)
track bike runs 30psi and 30psi.