On the scopes I've had apart the erector tube angles from a pivot point. The turrets provide a force one way, and a spring another.
One good reason for centering is that it's possible to lock up a scope if one of the turrets is at the edge of it's travel and another is then turned. Or that because one is at an extreme you may not get the full amount of travel in the other. Depends on the scope, but i've released a Nikko before under that very condition.
I don't see any harm in optical centering. I see far more issues with bending bits of ally.
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