The Idea is that if you want to make an Presentation, you might want to have
one window on the Notebook itself where your presentation is more detailed,
meaning you have more self produced notes so you don't fall literally out of
line. The other window should be for the Presentation itself which will be
projected via lets say an Projector. This means, while the customer or while
you are at a conference and you have to make a presentation, one might get
nervous and need hints on the presentation which would not look very good
that everybody can sees on the projector screen, but the screen the
presentator only sees is full of own notes, scribbles and other things to
keep the presentor in the track of what he wants to present. I hope I
explained it quite well.