Besides accentuating the calf (which is always visible when women choose to wear high-heels -- you never see them paired with an ankle-length skirt, unless the woman is totally naive about high-heels' intended use), it also re-angles the pelvis as Ladislaus said, all with the aim of being more sensual. Especially as she walks.
It's not attractive to me, because I think the woman is stupid, walking on such stilts in lieu of real practical shoes, and probably worldly, vain, etc. But that's just me :)
They are ridiculously impractical shoes for the women -- vain at best, an occasion of sin at worst. Not practical at all.
I wish I had a nickel for every movie scene where a woman is running for some reason, and has to take off her shoes -- invariably high-heels -- to be able to run at all.
That just shows how they fail as shoes.