I saw a documentry on tv regarding attractiveness. Although symmetrical faces were tended to be favored as more beautiful (at least in western society). It doesn't mean that a perfectly symmetrical face is physical perfection.
If you make a face perfectly symetical hoiztontally it isn't attractive. Photos were shown to demonstrate this. Perfect symetry looks freaky. Probably because noone's face is perfectly symmetrical.
Just thought I would add that to reinforce what John said.
That's great news for us. Because it is almost impossible to:
1) Cut the lace on the front hair line symmetrically.
2) Line hairline up perfectly (although i'd like to think I do a good job)
So get it as close being symetrical as you can and any imperfections you have will look natural.