An example of a well meaning volunteer messing things up -
(and I have admin permissions)
I lost my home page yesterday . . . the person editing another page somehow copied that html over the home page html and put 2 copies of their page on the website - no copy of the home page. Clicking the website url took you to that page instead of the home page.
Fortunately I had an html file from when I was developing the home page - I know there have been online changes since then, but at least it gives me a starting point. (She had edited it after installing it, so undo was no good.)
If the person's permissions concentrated them on their area only, they would not have been able to do it.
If we had the ability to rollback, I would have been able to just reinstate.