Gasket matching vs. port matching.

Why do you grind material away to reach the edge of the gasket?
Just asking an honest question. Sometimes the head intake port mismatch may only be a few thousandths of an inch or may even match without any grinding.
I'm thinking once you grind enough to take care of the mismatch, there is no reason to go any further.
in my case the cnc`d victor type heads were a fair amount bigger than the intake , could have got by with it I guess , but that aint my way , always want the max. ...