是可以当做构造函数来用的

var adder = new Function('a', 'b', 'return a + b');

// Call the function
adder(2, 6);
// > 8

区别的话，用构造函数生成的函数不会有闭包，他们只能访问自身作用域和全局作用域声明的变量和函数。其他详细的地方参考MDN

Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was called. This is different from using eval with code for a function expression.

var x = 10;

function createFunction1() {
    var x = 20;
    return new Function("return x;"); // this |x| refers global |x|
}

function createFunction2() {
    var x = 20;
    function f() {
        return x; // this |x| refers local |x| above
    }
    return f;
}

var f1 = createFunction1();
console.log(f1());          // 10
var f2 = createFunction2();
console.log(f2());          // 20