That Sierra massively boosts the tabs feature of macOS/OS X is not news, having been flagged heavily during the macOS Sierra keynote back in June. Put simply, many more apps now have tab bars just like Safari and Finder – everything from Notes, to Calendar, to Pages. Even third-party apps are supposed to be tab-compatible, even if they haven’t been updated.
What’s less obvious is a useful toggle within the Dock component of System Preferences. This lets you choose to default to opening tabs in apps, rather than opening a fresh window (see screenshot below). This is a particular help in Finder, where any request by an app or the operating system to spawn a new Finder window – if you’ve just mounted a DMG to install an app, for example – will result in a new Finder tab instead.
It’s not really clear at the moment how the new tab feature works within many apps. For example, there’s an option on the View menu within Calendar to show the tab bar, but I can’t see any way of creating a new tab. It’d be useful to have month view on one tab, for example, and week view on another.
It’s a similar story in the Mail app. Creating a new message creates a new window, even if the System Preferences option above is set to Always and the tab bar is set to be visible. Apparently clicking the Window > Merge All Windows option is supposed to combine all open windows into a tabbed interface, but some apps don’t have this option – and on those that do it just doesn’t work.
To be blunt, this feature feels a little unfinished.