We test to make sure everything electrical is insulated from the chassis, so people won't get shocks when touching our equipment, causing injury and in serious cases, death.
With the hi-pot test we run the probes between the hot and ground of the iec connector, and then the neutral and ground of the iec. We jack the tester up to 1300 vac for a period of 1 second. This test, in theory, shows that if that much current can't break the insulation, then nothing will.
james