According to the release notes, the update “improves the stability, compatibility, and security of your Mac.” The release notes also state that the update:
We always recommend that you back up your Mac before installing the update.
Roman Loyola
Apple releases OS X El Capitan 10.11.1 update
21.10.2015
Apple on Wednesday released an update to its Mac operating system, El Capitan. The 10.11.1 update is available in the App Store under Updates. You can also go to the Apple menu, select About This Mac, and click the Software Update button in the Overview window.