[mwgalloway]

Ok, but why should I even care about what was on this hypothetical blackboard? Do you have any real world examples with business or technical significance where this "cope with it, somehow" approach to mutability is a clear win?

[Joker_vD]

You've just stated it, no? If you only care what is on that blackboard right now, not what was there — why even bother storing knowledge about its previous states?