I agree, it's always been unsettling to see any[] on hover, even though it gets typed in the end.

I think one reason might be to allow the type to be refined differently in different code paths. For example:

    function x () {
        let arr = []
        if (Math.random() < 0.5) {
            arr.push(0)
            return arr
        } else {
            arr.push('0')
            return arr
        }
    }