While the iOS 10.2.1 update is light on new features, the security updates that comes with it are numerous. This update will fix some of the more commonly known vulnerabilities that can be found in the kernel, WebKit, and even the Contacts app.
One such example is a vulnerability in the WebKit that, if exploited, would allow for arbitrary code execution. A full list of the patched vulnerabilities can be found here.
Apart from vulnerabilities, the iOS 10.2.1 update has also fixed a buffer overflow bug that can be used to briefly gain access to the Home Screen of an Activation Locked iPad that has been reset recently. Another bug that was fixed is the Apple Watch’s Auto Unlock feature which triggers when the watch is removed from the user’s wrist.