On my own computers I typically have the two logins you mentioned, the user and the root account, since there's only one of me and only I use the computers. On the computer I recently had for work there were many accounts, since the sysadmins sometimes needed to SSH in. I also selectively added accounts for some of my coworkers as needed.

If I lived with any family, making non-sudoer accounts for them on at least some of the machines would seem like a pretty normal thing.

I use a locked down kiosk user account when I’m responsible for driving slideshows or videos for events. I restrict the permissions so that if someone were to access the laptop, they can’t make any meaningful changes or pull up something inappropriate. I also change the wallpaper and account icon to match the event.

I could use a cheap throwaway laptop, but actually using my M1 MacBook saved me. One time I was running a slideshow that lead into a new years countdown, somebody decided the laptop was in their way so they unplugged the power cable and moved it. It ran on battery for 6-7 hours before I noticed and nearly had a panic attack.

It depends on the computer. Some of them have multiple local accounts because they're used by multiple people. Most of them have an account for me and for root. In most of those, actually logging in as root is disabled, though.

Only mine. root only via sudo

Two, user and root, but I live alone and don't have to share with anyone.

On a mac and I have 1 user account for myself only.