“Even if you’re Mac is on the compatibility list, that doesn’t mean you can take advantage of all of the new features in Sierra. There are other things to consider,” Gil writes. “You’ll need a newer model Mac and a compatible iPhone or Apple Watch to use such things as Handoff, Auto Unlock, Siri, Apple Pay on the Web, Apple’s Continuity features, and more.”
“You should also have an iPhone 6 or newer running iOS 10,” Gil writes. “If you hope to use Auto Unlock, you also need a Mac that is from 2013 or newer and an Apple Watch running watchOS 3.”
Much more, with good instructions for those upgrading to macOS Sierra, here.
MacDailyNews Take: If your Mac is on the bubble of compatibility, think about partitioning your Mac or creating a bootable drive, so you can try macOS Sierra in tandem with OS X El Capitan.