组合功能的好处

I have four methods which alter the input and return the output.

class edit
{

    function a($input) { return $input + 4; }
    function b($input) { return $input - 2; }
    function c($input) { return $input * 10; }
    function d($input) { return $input / 8; }

}

Coincidentally these methods need to be called one after the other with the returned output from the previous as the input to the next.

We can handle this process multiple ways.

$handle = new edit();

$output = $handle->a(8);
$output = $handle->b($output);
$output = $handle->c($output);
$output = $handle->d($output);

or

create another method within the class to handle this entire procedure.

function all($input)
{
    $output = $this->a($input);
    $output = $this->b($output);
    $output = $this->c($output);
    $output = $this->d($output);
    return $output;
}

$handle = new edit(8);

$handle->all();

These both achieve the same task.

However, I have recently learned about composition functions, Which is perfect for I need to achieve.

(note for the example here I have moved the methods a,b,c,d from the class and will call them as functions in a procedural manor, I have been unable to make this composition function OOP friendly, please excuse me for this.)

function compose($f,$g,$h,$i) 
{
    return function($x) use ($f, $g, $h, $i) { return $f($g($h($i($x)))); };
}

$comp = compose('a', 'b','c','d');
$result = $comp(8); 

With all this being said, I want to know the benefit of achieving this task with the composition function?

I can only notice minimal improvement in that we do not have to pass the input four times, only once.

In my recent research, I have come across multiple software engineers talking about how great functional programming is.

I feel that I am missing something? Or is the only improvement what I mentioned?

PS - The language I use is PHP, The methods/functions I gave here are just simple examples to illustrate the point. I am also trying to adhere to SOLID principles.

Thanks.