Would you like to make time appear as an interval like "4 days 3 hours ago"? Possibly you have worked with such formatters (drupal time ago) in views and date fields, but what about editing a node.tpl.php for example? Or programmaticaly include the last login time of a node's author, as time ago, in a block?
It comes in handy when there is a reusable function to format our time statements as drupal time ago - and php in general. So here comes a little function to be included in the template.php file. You can easily use it in your themes to display a timestamp as "Time ago".