How can the array_diff function be used effectively in PHP to achieve the desired result?

To use the array_diff function effectively in PHP to achieve the desired result, you can compare two arrays and get the values that are present in the first array but not in the second array. This can be useful when you want to find the differences between two arrays or filter out common elements.

```php
$array1 = [1, 2, 3, 4, 5];
$array2 = [3, 4, 5, 6, 7];

$diff = array_diff($array1, $array2);

print_r($diff);
```

In this code snippet, the array_diff function is used to compare $array1 and $array2, and the values present in $array1 but not in $array2 are stored in the $diff variable. The print_r function is then used to display the elements in the $diff array.