Are there any best practices for optimizing PHP scripts that involve checking for key existence in arrays?

When checking for key existence in arrays in PHP, it is best to use the `isset()` function instead of `array_key_exists()` as it is faster and more concise. Additionally, you can use null coalescing operator (`??`) to provide a default value if the key does not exist in the array.

// Using isset() to check for key existence and provide a default value
$value = $array['key'] ?? 'default_value';