Local documents, when used with 3rd party systems, provide an alternative collaboration workflow. Paid plans fully support this solution as well as collaboration workflows within the Adobe XD platform."
That doesn't answer the question at all. Why are you removing this basic and essential feature?
Why should I support the company knowing they'll arbitrarily remove my ability to save my own work? What happens if I can't connect to the Cloud? Why should I trust Adobe to maintain the integrity of my files? If you're trying to block me from exporting XD to invision or marvel with a paywall, why block Saving instead of Exporting? This is a bad decision and should be seriously reconsidered.