If you are not using configuration templates and you make changes along the way, you can experience some configuration drift from the initial parameters and there is no way to go reverse all the changes at once.
We are addressing large Meraki organizations and MSPs who deal with multiple networks environment and for whom the native dashboard is too limited.
I think it happened once about two years ago that Meraki deleted parts of some organizations based on programming mistakes. I assume these customers had been happy to have a backup to apply.
Also, think about completely messing up your config. With a backup, you could easily go back. I wonder why Meraki does not have something like this build in the system. "Cloud" does not automatically mean the data is safe.