While presenting a slide show, you have tools like Presenter View that allow you to see your slides and notes while the audience sees the slide show. The typical setup allows you to face your audience while the slide show is presented on a screen behind your back to the audience. This allows you to see and connect with your audience while you are presenting. But when you want to show other documents, spreadsheets, and websites you need to move the window to the secondary display to show it there. Essentially, you lose the document window from your primary monitor and now you have to look at your slide show display to refer to it. You effectively lose your connection with your audience and worst of all your back is now facing the audience.