Why autoload classes?

Question

PHP

Why autoload classes? Just for convenience or does it save some other resources?
// There is a variant with a function

spl_autoload_register(function ($class) {
    include APP. '/' . $class . '.php';
});
$obj  = new MyClass();
$obj->myMethod();

There is an option through Composer
Or you can simply do 100 reqire_once () at the beginning of the file, indicating the class path. What is the difference in these methods?

Answer 1

It provides loading on demand , not these yours.
It's possible, but what for? Always drag everything everywhere. In addition, as long as you have one file in which the includes are made, it’s still all right. But there are projects larger than your site, where there are hundreds and thousands of files . It's very convenient to add another require_once() to a thousand files, right?