We are a completely residential company (except for some occasional very light commercial). Each site is an individual customer. Network configurations do not carry between sites in the controller software, so SSID's and passwords are configured on a site by site basis. The benefit of doing it this way is I can log in to one controller instance and click in the top right corner where it says "Current Site" and go directly to whichever customer's configuration I need to access.

Another benefit of doing things with an AWS instance is I can set up multiple "Super Admin" accounts who have access to all of the sites on the controller, so for example, in our company there are 3 of us who have access to the unifi controller, I just happen to be the one that set it up and manages it because I have the most networking/IT background. If someone quits or is fired, we are not using a shared login to be able to access it, so I can deactivate their account and not have to deal with changing user passwords, and adding a user if we hire someone else is just as easy. I can also see who logged in to the controller and made what changes as well. Any user with "Super Admin" privileges has access to any site created immediately, without having to be invited by the person who set it up.

If I were working as a network person for a company with only one location, I would absolutely use a Cloud Key as long as the instance didn't exceed the number of recommended devices on that network. And if that were the case, the company would probably have a local server running to be able to stick the Unifi controller in a VM any way.

I really need to take the time to write down all of the benefits of doing it this way for us, but I can't seem to think of them all at once...