It’s especially useful if you find a window is stuck off screen after disconnecting a monitor.

can’t recall if it’s out of the box or if I configured that

That’s out of the box. No configuration necessary. The default behaviour in Plasma when pressing the Windows key is to open the application menu where you can start typing to find what you want. In fact it’s kind of a pain to disable that, and will sometimes re-enable itself randomly as I recently found out (I prefer WIN+D to open the app menu from my i3 days, and I work in an RDP connection to a windows machine where I would prefer to be able to just press WIN to open that menu and not KDEs menu.)