In what scenarios would regular expressions be more effective than built-in PHP functions for removing characters from a string?

Regular expressions would be more effective than built-in PHP functions for removing characters from a string when the removal pattern is complex or non-standard. Regular expressions allow for more flexibility in defining the pattern of characters to be removed, making it easier to handle cases where the characters to be removed are not easily captured by a simple built-in function.

$string = "Hello, World!";
$pattern = '/[aeiou,]/'; // Define a regular expression pattern to remove vowels and commas
$filteredString = preg_replace($pattern, '', $string); // Use preg_replace to remove characters based on the pattern
echo $filteredString; // Output: "Hll Wrld!"