Pre-cook liver before frying?
It's not exactly the same for liver, but there is some reason to roast it before frying:
Some people believe in roasting (grilling) before the cooking/frying in order to make the blood drip out of the liver. Can do on fire or in an oven; doesn't matter.
Personally I prefer to go directly to the pan and just fry so it gets less dry. It is definitely sufficient cooking for the liver.