Continuity is now a major feature in OS X Yosemite. Basically, you can now switch between Apples devices that are near one another simply and smoothly. It means hot spots are set up more easily, and you can switch from your desktop to your laptop to your tablet to your phone very quickly.
If you are looking at a website on your desktop, then pick up your iPad next to you, you can swipe up on the lock screen to open the same Safari window you were looking at on the desktop. It's all one seamless search experience between devices.
The major use case being pushed: phone calls. Say you want to call a friend. You can look up the name in Spotlight on your desktop, and find their contact, then dial the number. You can also dial from web pages.
Craig Federighi, Senior VP of Software Engineering decided show off the feature by calling a new Apple hire in the middle of his presentation: Dr. Dre.
One of the best features of OS X: there's going to be a public beta program. Sign up here.