According to the release notes, this update addresses the following issues:
Fixes an issue where audio and haptic feedback would not work on some iPhone 7 and 7 Plus devices
Addresses an issue where touch input was unresponsive on some iPhone 6s displays because they were not serviced with genuine Apple parts
The release notes go on to say that non-genuine replacement displays "may have compromised visual quality and may fail to work correctly." Luckily, for those whose iPhones were repaired using non-genuine parts, Apple has issued a fix for the problem that will bring their handsets back to life.
Since there's no mention of performance or battery-related fixes, it's likely that these issues will have to wait for iOS 11.1, which is currently available for beta testers.
iOS 11 annoyances, and how to fix them
To download the update, go Settings > General > Software Update (the preferred way, and it's about 300MB), or connect your iPhone to a computer running iTunes and then carry out the update (this is slower and downloads the entire operating system as opposed to just the changes, and it comes in at several gigabytes).