Aside from securty, it can be a good presentation tool.
I just used my PB to run an iPhoto slide show, then present a, and then by using a screen saver slide show (and a quick corner) go back to a simple slide show, all seamlessly with out using a an AV switcher or showing more than a moment of a mouse move. I could have used iTunes for the lead in and lead out music, instead I used my iPod. Some LCD projectors go to sleep (ours looses the keystone settings) if nothing active happens on the screen for a time, so for me the screen saver serves as a good tool.