For the record, when you see cranksets labeled as 172.5 or 175 cranks, it merely is referring to the length of the crank arms. This was documented earlier, and regarding what the difference is between the two cranks, it is very minimal.
When you take into consideration that 2.5 millimeters are not even 0.1 inches, it becomes clear that the difference in distance is quite minute. Then again, it can still make somewhat of a difference.