Ad Hoc Networks
Why do we need ad-hoc networks?
More laptop users
More smartphones users (e.g.. Android phones, iPhones)
More devices with Wi-Fi-support (e.g.. televisions, hi-fi, home-theaters, media servers etc.)
Moving users, vehicles, etc.
Outdoors places

In all these occasions there is no centralized infrastructure (such APs)
So ad-hoc network is a necessity