I think i read somewhere that facial symmetry is a sign of genetic superiority or good genes in general. Humans are innately attracted to others that will breed the best offspring possible. Thats the only reason people would find it important
It is hard to say honestly because as far as I have heard the symmetry is subconscious perception and facial features is a conscious level perception so I don't think I could say correctly because one is an instinctive reaction.
No there was a girl I used to work with who was born with an asymmetrical face and she told me when she was a baby she had to wear some special helmet to squeeze it into shape as she grew. She was really fucking hot man! ahaa