Compression ratio too high for 91 octane?

I for one don't understand why you would build a motor on the razor's edge of detonation? Can it be done possibly, maybe, certainly, (why)it seems like way too much to lose for the gain. Unless possibly you're building the motor for competition and are being dictated by class regulations? Overheating, lean condition, a change in timing it seems all of this could lead to catastrophic engine failure.