Yeah, it depends a lot on how your existing system is configured, whether or not you start from scratch, and which setup page the setup assistant lands on. I've done migrations where the iCloud Drive setup page shows up, and not. It's not consistent, and Apple does a terrible job documenting how the system works and why.
Also, unless you are buying extra storage (which Apple clearly wants you to do, thus all of the default crap), your iCloud Drive Desktop and Documents setting can very quickly stuff iCloud full and then you'll start getting the feed-the-beast prompts. People get confused and feed without asking and then get roped into paying for something they might not actually want.
I don't like it at all. So, when I do migrations, I make sure that setting is checked off. Then, the customer can turn it on if they want. It's cryptic, and I think it's designed that way intentionally because it helps sell online storage to people who have no idea what's happening.
I refuse to use it.
Quick point: If you use iCloud Desktop and Documents, you can still use the service without internet access because all of the files are stored locally in the [well-hidden] Library. Then, when you get online the system will sync any changes. But, again, it's cryptic how and why this works, and even more cryptic that signing out of iCloud removes the files from your local drive.
Moral of the story: Use it when you know what it's doing, and the repercussions to turning it off.