It's a step above a pattern/PIN lock; with a minimum drop in convenience. No smudge trails left on the screen, can't be easily guessed, and you have to know who the owner is before you can unlock it. Not as secure as, say, a fingerprint scanner, but it's also easy to implement on existing devices.
i think the parent was talking about the security implications of having your unlock pattern show up on the screen. it's entirely possible to not touch the screen enough after unlocking to wipe out your pattern.
