Shell scripts let your scripts interact with other programs on your server. E.g. use Image Magick to manipulate images, run Linux’s uptime command to check on your server load.
<?lc put shell("dir") // fires off windows dir command and outputs the results ?>
Being able to execute commands like uptime is particularly useful as you can build a variety of simple apps that let you monitor the health of your server(s) from you phone, tablet or desktop. You can even trigger SMS’s or warning emails if for example the load on server starts to get to high.