REALLY OVERTHINKING 0 moa / 20 moa rails

[Dirtrax]

What, pray tell, IS the advantage of 'optical centering'? And *** does 'optimal performance' mean? If your scope does not 'perform optimally' while dialling, why even bother having one? Everything below your zero is totally useless, while having more above, lets you play farther.

Others have done a good job of explaining it (thank you koda). Scopes align multiple lenses especially in the case of adjustable parallax. The better they align the better the quality of the image. It's not rocket science.
EDITED to especially.

 

[ARlife4me]

ring height can do 2 things, give clearance for the objective and best focal points. you can have 1 and not the other w/o a cheek riser. keeping as close to the barrel is best. look at your optic specs (lets say 30 moa elevation) it'll give you 300" (25') @ 1k yards. does your cartridge have enough to be within that range w/o adding 20 moa rail (500"+ 41' 9") of drop. on 1 rifle it came with a 20moa rail, then the mount was a 20 moa. 1st thought it would be 40 moa...............nope, it's 400 moa. you multiply it instead of adding. now my 400 moa combined rail/mount + the 120 moa optic has way more elevation than it'll shoot (savage 110 24" 338lm). 5,200" @ 1k is like mortaring it there