Continuity, including Handoff, Universal Clipboard, Cellular Calls, SMS/MMS, Instant Hotspot, Auto Unlock – requirements and how to set each up. Note that most need both Bluetooth and WiFi to be turned on: if your Mac only has wired Ethernet enabled, features will not work fully (or at all).
Sierra Help online – the same content as is delivered by the Help menu.
Using Siri on your Mac.
Optimised Storage – new features to store files in iCloud, and perform housekeeping accessed through About This Mac, in the Storage tab.
Supported printers, scanners, and faxes – although this list does not yet specify which are supported in Sierra, the implication is that those listed are.