Accidentally mutating globals was a big problem with the language. Const didn't solve it completely: you can still implicitly create globals by forgetting to declare the binding locally. But at least if you have a global you can make it an immutable binding and get warned about mutating it some of the time (ie assignments). As far as I'm concerned that is all it is useful for. For a local binding you don't really get much benefit since it's not deeply immutable, and it isn't an improvement to the ambiguity of local/global scopes, so you're frankly better off not using it as it will trick newcomers.

The same argument doesn't apply to Data's shallow immutability. It will give you errors when mutating at least some of the fields. If your code can catch you mutating a number, then you can notice the bug and be reminded to make deep copies etc. It's an improvement, just like Object.freeze.