This is another feature that many phone users never bother to turn off, unaware that the battery is eating itself alive, as the handset listens for open Wifi connections. And just like with Bluetooth, there's no excuse – that same quick-access settings menu has a tappable Wifi icon.
Also, make sure the default state is off (the icon will go dark). After all, the halcyon days of readily available, password-unprotected Wifi are over, so you generally know when such a connection is possible. The only exception is when you're using a navigation-related app, since nearby Wifi signals, even when they're rejecting your phone's desperate plea for connection, can assist GPS in accurately pinpointing the device's current location.