In my career, when I was meeting a new PHP developer or working on any project, I haven't seen too many people using '&' in front of a parameter name.

Even when I started my adventure with PHP, I didn't hear about it. I think this is a great time to remind the community about the "&".

Ind documentation we can read

You can pass a variable by reference to a function so the function can modify the variable

function foo(&$var)
{
    $var++;
}

$a=5;
foo($a); // $a is 6 here

This means that the function gets a reference to the original value of $var, not a copy of that value. Example:

function more(&$num) { $num++; }

$number = 0;
more($number);
echo $number; // this outputs "1"