Find My iPhone is a component of the Find My application, which Apple preloads on iDevices, and iCloud.com. It enables users to track their lost device. If you end up losing your iPhone, then you can take advantage of Find My app on another Apple device to check its last know location.
Moreover, Find My iPhone is a way to make your iDevice less appealing to steal as you know probably know. Once Find My is turned on an iPhone or any other Apple device, the device can’t be unlocked without iCloud passcode of the original account.