Version control can be built into the system. One click to deploy the change, one click to revert it. (You could even have automatic one-box/A-B deployment of a change within code)
You end up building an ad-hoc, informally specified, slow implementation of half of a regular development environment "inside" your system. These "closed world" systems can do some amazing things, but it's very rarely enough to make up for not being able to work with standard tools from outside the ecosystem.
