Apple wants users to be able to smoothly move between their Macs and iOS devices. AirDrop now interoperates between Mac and iOS devices. However, it goes further. Handoff allows you to send a document from your Mac to your iOS device, just by being in close proximity to each other.
The Mac also notices when an iOS device is nearby for Personal Hotspot. The phone appears in the WiFi menu, shown above, and with one-click the phone connects to the Mac and the devices start tethering.
Handoff also works in reverse. An icon appears on the iOS lock screen, swipe up and it flows between the iOS device and the Mac. It’s probably best described as an impromptu AirDrop, with whatever documents and data you are currently working on.