the best explanation would be, a perceived kind of pseudo uniformity that high % gives you
https://www.mouse-sensitivity.com/forums/topic/4704-conversion-method-guide-and-other-faqs/?tab=comments#comment-18180
and no generally id use 0% whenever possible (even if that means hat i can only properly match 1 scope which in those kind of games doesn't really impact you all that much since hipfire would be 90%of firefights regardless)