A really useful feature in case you want to receive a warning notification before you use all of the mobile data available according to your mobile provider contract. It's a great way to avoid additional charges.
In case you just upgraded your iOS powered device to iO7 or any other version and now this device runs slower than it used to, this resetting of the device procedure might speed things up.
Very useful Android feature can turn your Android smartphone into a Wireless hotspot that enables other WiFi devices like laptops or other smartphones to use your Android phone's Intenet connection.