This not only increases the execution time but also makes the coding long and complex.
For example,
<?php
If (condition1==true){
code which satisfies the above condition
} else {
perform die(); or exit();
}
?>
The same set of codes can be written as:
<?

if(!condition){
// display warning message.
die("Invalid statement");
}
?>
This reduces the execution time and also makes the codes easily maintainable.you can use www.W3School.com for help.