That, of course, won’t affect how other apps interact with the multiple screens, so that’s not a global solution. If you’re using Keynote for your presentation, you can actually specify which of multiple screens you want as the presentation screen and which you want as the speaker notes screen (if you’re not using mirroring) which can be really helpful as the speaker’s screen has a clock, timer, preview of the next slide, etc. That is curious because in my experience, Mac OS is very good at keeping your standard screen as the main screen, menu bar and all, with any secondary displays that are plugged in - via USB, HDMI, Thunderbolt or DVI - being additional screen real estate, but never becoming the new main screen.
