PHP call_user_func vs. just calling function

I'm sure there's a very easy explanation for this. What is the difference between this:

function barber($type){
    echo "You wanted a $type haircut, no problem\n";
}
call_user_func('barber', "mushroom");
call_user_func('barber', "shave");

... and this (and what are the benefits?):

function barber($type){
    echo "You wanted a $type haircut, no problem\n";
}
barber('mushroom');
barber('shave');

Always use the actual function name when you know it.

call_user_func is for calling functions whose name you don't know ahead of time but it is much less efficient since the program has to lookup the function at runtime.

Although you can call variable function names this way:

function printIt($str) { print($str); }

$funcname = 'printIt';
$funcname('Hello world!');

there are cases where you don't know how many arguments you're passing. Consider the following:

function someFunc() {
  $args = func_get_args();
  // do something
}

call_user_func_array('someFunc',array('one','two','three'));

It's also handy for calling static and object methods, respectively:

call_user_func(array('someClass','someFunc'),$arg);
call_user_func(array($myObj,'someFunc'),$arg);

the call_user_func option is there so you can do things like:

$dynamicFunctionName = "barber";

call_user_func($dynamicFunctionName, 'mushroom');

where the dynamicFunctionName string could be more exciting and generated at run-time. You shouldn't use call_user_func unless you have to, because it is slower.

I imagine it is useful for calling a function that you don't know the name of in advance... Something like:

switch($value):
{
  case 7:
  $func = 'run';
  break;
  default:
  $func = 'stop';
  break;
}

call_user_func($func, 'stuff');

With PHP 7 you can use the nicer variable-function syntax everywhere. It works with static/instance functions, and it can take an array of parameters. More info at https://trowski.com/2015/06/20/php-callable-paradox

$ret = $callable(...$params);