It lets you customize for example the max memory available for the PHP scripts, or the maximum execution time, or whatever PHP settings you need to edit.

Useful in particular to do quick/temporary edits, or when you don't have access to the PHP.ini file (like on some shared hosting).

What PHP settings can you modify? Those marked with PHPINIALL in this list (i.e. uploadmaxfilesize & postmaxsize are not modifiable)

Examples of what can it be used for:


Fix problems caused by misconfigured PHP settings, when the hosting provider does not let you change them in an easy way
Customize the error reporting level, hide errors from your site
Set the PHP timezone