The Messages app on your iPhone can quickly grow to be one of your biggest storage hogs, especially if your friends use it to share a lot of photos with you. If after taking a look at Settings -> General -> iPhone Storage you decide you want to start deleting message threads to free up storage, you probably will want to keep some of the images in those threads.
iOS fans have been clamoring for a "dark mode" feature for a long time now. A true dark mode feature would change the colors and brightness of certain areas of the screen, making it more suitable for dark environments like movie theaters, where a bright screen is liable to annoy fellow movie goers. This is different than Night Shift, which reduces eye stress caused by blue light by shifting the display to the red end of the spectrum.
With every new iOS release come several new features that Apple enthusiastically introduces during its annual WWDC event, while a plethora of smaller features go unmentioned. The introduction of iOS 11 followed suit, spotlighting major changes to Control Center and screen shots, new AirPod controls and Screen Recording.
In addition to adding the Loop, Bounce and Long Exposure effects to Live Photos, iOS 11 introduces several new editing features. You can now trim them and change the key photo, which is the photo that displays in your album.
iOS 11 has finally added a way of shutting down and rebooting your iPhone or iPad without having to press the Home or Sleep/Wake buttons, which should be a welcome feature for those with malfunctioning buttons. The reboot button is buried annoyingly deep in the Accessibility features while the new Shut Down button is easily found in Settings. Here's how to do both: