What role does the "session_start" function play in PHP scripts, and why is it necessary to include it in every file that deals with sessions?

The "session_start" function in PHP scripts initializes a session or resumes the current one. It is necessary to include this function in every file that deals with sessions because it allows the script to access session variables and ensures that the session is started before any session data is accessed or modified.

<?php
session_start();

// Your PHP code that deals with sessions goes here
?>