Meaning of covered-buffers when splitting window

[mobid]

Hi,

If have next case:

1. Start in scratch buffer
2. Open two X windows, one above the other
3. Now when I split window I expect covered X window to be shown, instead scratch is displayed in other window.

As I saw in code https://github.com/emacs-exwm/exwm/blob/master/exwm-layout.el#L392 there is case which prevent my expected behavior. If I set there covered-buffers to nil it is working fine for me.

Is there any case when covered-buffers are meaningful?