You can instruct your Mac to cache software updates, app downloads and iCloud content so the other devices on your home network can access these quickly. This works best if you have plenty of hard drive space to spare and many Apple devices in your home.
You get to it in System Preferences by going to Sharing and then look for Content Caching on the left. I have it turned on here and you can see the green light is on which won't come on right away. It takes a little while to get started. Basically what Content Caching does is it will store local copies of things like Mac OS Updates, App downloads. Even your iCloud data like files and photos and things like that on your Mac's hard drive.
So you only want to do this if you have a Mac that has a large hard drive. If you already are limited with space on say a MacBook or something then this isn't for you. But if you have a desktop Mac and it has a big hard drive and you have plenty of extra space then you can use this. You can also use an external drive. You go to Options here and you can edit the cache location and use an external drive for this. You can limit how much space is used for this cache on your drive. Unlimited allows your Mac to just basically manage it itself and use any extra space available. But if I limit it all the way down to 2 GB then it will basically only have the latest stuff on there and maybe get rid of stuff it doesn't think it needs anymore.
Basically you can set it to All Content, Shared Content, or only iCloud Content. Shared Content would be things like Mac OS updates. Also iPhone updates and things like that will be stored as well. Also apps. iCloud Content would be things like your files and photos. Now think how great this is if you use iCloud Photo Library you may have everything on your Mac and able to view it there easily. But on your iPhone you're just pulling the photos from the internet as you browse through them. If you're in your house, this way it's getting those photos actually from your Mac, not actually pulling them all the way from iCloud. So it would be a lot faster because typically the network in your house is a whole level of magnitude or two faster than actually accessing data on the internet. So this is a really handy function to be able to have especially if you have a Mac like mine that has plenty of hard drive space.
Apple has all sorts of information about the details of this feature. So you can find it here. I'll include a link to this on the MacMost post. They detail what Content Caching is. How it works. It gives some examples and things like that. Even some complex situations and how it works. So it tells you all this information. Also it tells you about how you can view the logs for it and statistics for it.
One way to do that is to go to the Activity Monitor. Under Activity Monitor you can actually switch to Cache which is only there if you have Content Caching turned on. This shows you things like in the last thirty days, seven days, and twenty-four hours how much the cache has been used. So you can see if it's getting used. If it's actually helping you.
So you can read a lot more about this feature. You can enable it if you want and speed up downloads. This is especially great if you have a lot of hard drive space and if you have lots of Apple devices in your house.
Apple’s support document: About Content Caching