They're designed for fast egress so you don't burn alive trying to get the ʞ©$ɟing thing off. If it's a proper, FIA certified harness then it should be a piece of cake to get out of it. Most of the high end belts have a rotary cam buckle, when you turn it all of the belts pop off at the same time with almost zero force required.
Of course its probably sensible to keep a belt cutter within reach in case the buckle is damaged.