Optical centering

[buttloaves]

I was reading an article in one of the mags about centering your scope before fitting to your gun, i would have thought the cross hairs will finish up in the same place regardless of where they started from. I always just put it on and see where it is and adjust from there, never had any problems, any thoughts? Don't string me up..
The hirsute gent in the mag was sporting an impressive full set.
He should don a bretton cap, he'd look like captain haddock, no offence intended..