There will always be times when your only choice is to work on your iPhone, iPad, or Mac simply because that's the only device at hand. But when you have multiple options--and many of us increasingly do--this opens avenues for working more efficiently.
In the particular case of Continuity and Handoff on the Mac, a key benefit is the integration with the iPhone. Not only can you answer and make calls to a linked iPhone, but also easily use the iPhone as a hotspot when you don't have an available Wi-Fi network (this requires a tethering plan with your carrier), and the ability to reply to incoming SMS messages. Of course if you're also the kind of person who starts long email messages on the iPhone and are frustrated by its small keys, having the chance to pass that message off to your Mac when you're within range of it will also be beneficial.
The way forward
Again, these two broad efforts indicate a direction Apple is headed--the way the company thinks about the future of computing, which is increasingly mobile and integrated. Contrary to past fears, OS X hasn't been replaced by iOS (nor the other way round) but rather Apple seeks to find the best use for each, with the cloud providing the glue that holds them together.
If you're the kind of person who is suspicious of cloud computing or simply want each device to exclusively own the data on it, Yosemite may not be for you. Then again, Mavericks and, perhaps, Mountain Lion, probably weren't either. Apple's been building this bridge for a long time. Nothing prevents you from opting out of the cloud, but gaining the full benefits of today's media and technology is going to become increasingly difficult (and less rich) without it.
The smaller picture
And then there are the littler things that too-often garner the greatest attention when a new operating system is unleashed.
In this particular release there will be people who object to Yosemite's new "flat" look. Gone are the 3D elements of old--the Dock that presented objects on a shelf, the bubbled buttons, the shadows. The system font has been slimmed down and translucency is more evident, used by default in Finder window sidebars and in the dock. Within the Accessibility system preference, you can make the interface more opaque by enabling the Reduce Transparency option and make text more legible by switching on the Increase Contrast option, but other than that there's very little you can do about the new look. If, after all this time, you still hate iOS 7's design, you're unlikely to be happy with Yosemite's interface.
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