Presumably you would not be using it as frequently as the 'right' mapping, i.e. it's mapped to some not super-common but useful editor function in a similar man

Presumably you would not be using it as frequently as the 'right' mapping, i.e. it's mapped to some not super-common but useful editor function in a similar manner to ctrl-, alt-, or meta- would be. Such mappings do not generally need to be optimised for speed or ergonomics as much as keys used for entering the text itself (and indeed using the 'wrong' shift key could still be faster or more ergonomic than using any of the other modifiers, depending on your layout).