Validating data from the client should always be done on the server in that context, regardless of if state is being saved client side or not. I think this is just an extension of what you said though.
I can think of many apps that don't need server side data storage or security that would benefit from this type of state saving however. For example, this app that I was using today - https://wheelofnames.com/ . Right now to save I need to create an account, presumably to tie my account to the saved state on the server side. That's pretty heavy/intrusive when all I want to do is keep the names list and preferences populated for my next visit.
Sure, there are reasonable use cases. It's worth pointing out where those use cases are not reasonable though, because those devs that don't know better will be inclined to treat obfuscated inputs as if they're trustworthy.
I can think of many apps that don't need server side data storage or security that would benefit from this type of state saving however. For example, this app that I was using today - https://wheelofnames.com/ . Right now to save I need to create an account, presumably to tie my account to the saved state on the server side. That's pretty heavy/intrusive when all I want to do is keep the names list and preferences populated for my next visit.