Xsleep opens up an X connection, sleeps for the specified number of seconds, and then closes the connection and exits.
Why do something so silly? Well I'll tell you. It's because many X servers reset themselves when they have no connections. This is a pain when you're starting up a session, because you do an xset, an xrdb, an xmodmap, etc., and between each one the server resets itself. So to prevent this, do an "xsleep 30 &" first, then your initializations, then start up your real clients.