What are the potential drawbacks of using require_once to include files in PHP?

Using require_once in PHP can slow down the performance of your application as it has to check if the file has already been included before including it again. To solve this issue, you can use require instead of require_once if you are sure that the file will not be included multiple times.

// Instead of using require_once, use require if the file will not be included multiple times
require 'file.php';