Happens across an KDE version.

Say you click a bunch of programs from your panel to load, and then you go back to typing away in your web browser. Those applications will come to the front, in the way of what you were doing and steal focus.

It's incredibly annoying from a usability point of view, and could even end up causing security issues. Say you're entering a password into something but you loaded a chat app, and boom it arrives to the front and you've sent your password to the chat instead.