How can I turn on / off AirDrop?

You should disable AirDrop if you don't use the wireless peer-to-peer file sharing feature often. Doing so will stop your phone from constantly searching for other iPhones or iPads nearby, and help you get more use out of your battery. You can disable this feature by opening Control Center (swipe up from the bottom of your display), and double tapping on the AirDrop logo.