xp is a command-line utility that takes all arguments and executes them as a command by itself, then pops up the results using kdialog. Its purpose is to make it easy to see the results of a program without starting a terminal.
I suggest having the run command applet on one of your KDE bars if you want to use this because it was really that applet that inspired this script. This script adds more convenience to the run applet.
No, it makes no sense at all to run this in command line, but embedded in other scripts it may if you want to pop up a dialog. (I did for my apcupsd onbattery script to pop-up a message about it).