Get app shortcuts with 3D Touch
A lot's been said about what's arguably the most useful new feature on the phone, and for good reason. The 6S's screen recognizes variations in pressure from your finger, which means you can do a lot of new stuff, most notably press and hold app icons to get quick access to popular functions. For instance, if you want to compose a new message, holding down the Mail icon opens a shortcut menu so you can jump right to it. Right now, the feature's mostly available on Apple's native apps, but there's no doubt developers will be taking advantage of this.
Peek at links and messages without opening them
Want to see what the gist of an email is without loading the full message? Tap and hold it, and a preview pops up. It also works for links within a message or text -- pressing and holding a hyperlink or street address gives you a glance at the web page or map, before you decide to actually open it.