Following the release of iOS 10.2.1, Apple has stopped signing iOS 10.2 firmware files thereby making it impossible for iPhone and iPad owners to downgrade to it.
With Yalu 10.2 jailbreak available only for iOS 10.2, this means that 64-bit iPhone and iPad owners who have already updated to iOS 10.2.1 will not be able to restore their device to iOS 10.2 to jailbreak it unless they had already saved the required SHSH blobs. Since Yalu 10.2 jailbreak is not available for the iPhone 7 and iPhone 7 Plus, owners of these devices have very little reason to downgrade to it.
If you have not already saved the SHSH blobs for iOS 10.2 for your device, you cannot save it now since Apple has stopped signing the firmware.
iOS 10.2.1 is a relatively minor update when compared to iOS 10.2 and only contains some security patches and bug fixes.
Apple has already released the first beta of iOS 10.3 which comes with a number of new features including Find My AirPods, user security section in Settings, APFS, and more. The final version of the OS is expected to be released in March.