PHP notice errors are sometimes frustrating and you are tired of seeing them when you are working on your scripts. They are showed at the beginning of your pages and may reveal confidential information to the visitor like the path to the file or the php file name (in case you are using friendly URLs).
There are cases when they are useful (for instance when you defined a constant twice or when you use a variable that hasn’t been defined), but there are situations when everything works fine on your site and you don’t really need them. Here’s the code that you should use:
error_reporting (E_ALL ^ E_NOTICE); /* 1st line (recommended) */
NOTE: Many programmers make mistakes while working on large applications so if there are cases when something is not working right on your site and you hided the notice errors, consider turning them on. They might tell you some bugs in your scripts.