The update fixes bugs and improves performance on older devices.
Apple is continuing its efforts to improve the experience offered by the latest version of iOS with the release of iOS 8.1.1. Available for all devices running iOS 8, 8.1.1 focuses on fixing bugs, though Apple hasn’t listed exactly what bugs are fixed by the update. 8.1.1 also brings performance improvements for older devices, namely the iPhone 4s and iPad 2, both of which were affected by iOS 8 thanks to their now outdated hardware.
As noted by ArsTechnica, performance should also improve on the first-generation iPad mini and the fifth-generation iPod Touch, both of which feature hardware similar to the iPhone 4S and iPad 2 (though it’s likely Apple made device-specific improvements that won’t be felt on every device.) iOS 8.1.1 is available over the air for the iPhone 6, iPhone 6 Plus, iPhone 5s, iPhone 5c, iPhone 5, iPhone 4s, iPad Air, iPad mini with Retina display, iPad mini, iPad (third- and fourth-generation), iPad 2 and fifth-generation iPod touch, and can be grabbed from the Settings » General » Software update menu.