The first is probably the most important to the security of your device. After it was discovered wi-fi on Apple, Google, and other devices were vulnerable, this update includes fixes that protects you from having your sensitive data (like passwords) decoded.
The second is more interesting to the audio-video buffs out there, but you'll have to wait a little longer for it: tvOS 11.2 will let users force the set-top box to match the HDR settings of the content they're watching, rather than have it default to the fastest frame rate.
Why would you want this? Well, it can cause issues on TV sets compatible with both HDR and Dolby Vision. If your set will play either 60Hz HDR10 or 30Hz Dolby Vision, your Apple TV will default to the former regardless of how visually pleasing the latter might be.
While tvOS 11.1 is available now, we'll probably have to wait a few weeks before tvOS 11.2. Still, something to look forward to for Christmas - and watching all the new Blu-ray acquisitions that are on your list...