Currying makes it implicit, but it's the same thing.

    const one = curriedSum(1)
    one(2)

is the same as

    const one = sum.bind(null, 1)
    one(2)

with the exception that the latter is explicit and not as slow as `curriedSum`.

Both `sum` and `curriedSum` can be used the same way:

    curriedSum(1)(2)
    sum.bind(null, 1)(2)

or just:

    curriedSum(1, 2)
    sum(1, 2)

One of the advantages is that non-curried functions make the return value explicit. You can't implement `sum(...addends)` with currying because curried functions have a fixed number of parameters. Once past that, a call will not return a function anymore.

    sum.bind(null, 1).bind(null, 2).bind(null, 3).bind(null, 4) // Still not called
    curriedSum(1)(2)(3)(4) // Maybe it works, maybe undefined is not a function