The main benefit of let/const over var is that it's block scoped. The benefit of const over let is pretty much nothing, much. It only prevents some limited form of re-binding. You can still easily re-bind const variables from inside a function:

    const x = 1;
    (function() {
        const x = 2;
        console.log(x);
    })()

or from an argument:

    const x = 1;
    (function(x) {
        console.log(x);
    })(2)

So it has limited value in any code that uses closures.