Yeah basically small snippets of reusable code are what functions are. If you see something you think can be used again somewhere else in your script, make it a function. I'd say have a minimum of 3 executable lines of code as a minimum. I've seen people use functions to shorten a function name, and while it's handy, it's hardly needed really
examples
function pr($expression, $return = false) {
return print_r($expression, $return);
}
function mres($data) {
return mysql_real_escape_string($data);
}
They're kinda handy for the users that don't have a good PHP ide but for those that do it's pointless with intelli code popups, snippet shortcuts and auto replaces