I used an app that did this a long time ago at a previous job. We were encouraged to explore the internet at first, but over time, we ended up restricted to only looking up the weather forecast, so a loading screen was quite useful when the boss walked in while I was checking email or playing solitaire. Jeff Lofvers of Don't Hit Save has a more dedicated reason for using his: to hide the fact that he's been at home playing video games all day instead of producing something useful.