If you centre your crosshairs (I prefer the mirror method) then use adjustable mounts to zero your rifle, you will have the best possible chance of optic perfection. i.e. you will be looking 'straight' through the scope at your target. Absolute minimum parralex and absolute maximum light transmission.
I don't Do It. I optically centre, then bung it on some sportsmatch mounts and zero it.. then again, I'm not striving for perfection