actually my question sounds like dumb question to you but I have some doubt about callback

function a(fn){
 Console.log(1,2,3)
  fn()
}

function b(){
console.log(4,5,6)
}

a(b)
//Output
//1,2,3
//4,5,6

But I can do this kind of same thing by following approach

function a(){
 Console.log(1,2,3)
  fn()
}

function b(){
console.log(4,5,6)
}
a()
b()
//Output
//1,2,3
//4,5,6

I have already mentioned that my question look like dumb to you but what's the difference between this two approaches and what's the benefits or drawback using callback here. Thankyou