The only test I have been able to conduct is an update to my Apple Watch. I click on update on my iPhone expecting a delay of several minutes while the update was downloaded from Apple's servers, instead the actual installation began within a few seconds — apparently it had already been cached on my server where I had set up Content Caching. My wife updated her Apple Watch today and had a similar experience.
The devices must be running
at least MacOS 10.13.4, iOS 11.3, Watch OS 4.2, or TVOS 11.3. (I think I have all the OS version numbers correct but I am not certain about TVOS), and they must all be on the same LAN (Local Area Network).
My internet download speed is generally in the vicinity of 66Mbps and my WiFi network theoretically tops out at 866Mbps. So even if I were using high speed ethernet for my LAN the downloads could not be any faster than I am getting with my WiFi connection because the choke point is Spectrum's cable and their servers, not my LAN. Transferring data between devices on my LAN would be faster which would be a plus for Content Caching. By-the-way actual download speeds from the App Store seldom get anywhere close to the 66Mbps available from my ISP due to the speed of Apple's servers, the instantaneous load factors on those servers, and how internet traffic routing is managed.
You might check out
this CultOfMac article. You will find instructions for setting it up in
this Mac Help Note. For really complex Content Caching situations see
this Apple Knowledge Base article and follow the "See Also" links at the bottom of the article.
In my case Content Caching is a particular boon because I have it set to cache
ALL content which included not only App Store content but iTunes Store, as well as iCloud content such as photos and Documents.
