Although using the $GET, $POST, $SESSION, $COOKIE, $_SERVER global variables makes things long winded - it increases portability as well as reducing the likely attack of SQL injection, as well as substitution of proper values in your code...
It is turned off by default for security reasons, although it adds to the code, it makes it that much more secure as well as letting you know where the actual variable is from.
Although the code shown below is good, it doesn't cover all of the above - especially if you are used to calling $cookieval for cookies for example - or $sessionval for that matter...