Leveling a Scope Vital or Not?

[mr ed]

Admitting my ignorance here. I can understand how unlevel crosshairs could affect bullet impact if the gun is shot by more than one person, since some will cant the rifle to get the crosshairs level, and others won't. But for a single shooter, if he/she uses the same cheekweld etc for each shot, why would it matter if the crosshairs are at 45 degree angles, or 60 degree or whatever.
I'm talking about a simple X or duplex crosshair, not the ones with mil-dots or BDC circles or all that fancy stuff.

Back in the olden days before everybody became an internet gun expert. I used to have a lot of customers who wanted their scopes zeroed with the crosshairs X instead of +.
They claimed faster shots and clearer view of what was behind those thick 70's-80's crosshairs.
kind of a pain to adjust though.

Mostly on 100yd 30-30 deer rifles not long distance guns.