Mouthpiece symmetry???

An apology if this is repeating any previous posts, though I couldn't find this info when I searched.

A few questions about mouthpiece symmetry:

I am curious to know at what point it becomes pointless to pursue absolutely perfect symmetry when refacing. HR pieces seem to be harder to get perfectly symmetrical, maybe because of the softness of HR compared to metal, and the unforgiving ease with which HR changes. But anyway, I am just wondering what differences marginal non-symmetricalness actually makes. I can understand that the tip and tip rails need to be as close to perfect as humanly possible, given that this is the part of the mouthpiece that interacts with the reed, but what difference does, for instance, a slightly non-symmetrical window bottom curve have on how the mouthpiece performs?

Cheers guys –
Christian Watson