The Picasso has a built-in monitor switcher, meaning you can plug the Amiga's output into the Picasso's input and the Picasso output will automatically switch between them depending on which kind of screen is frontmost. It's a fantastic feature and it's incredibly unfortunate that the more recent graphics cards don't have it.
Point being, you don't need two screens (provided your Amiga's output is scandoubled or your VGA monitor is 15KHz-capable).
With 2 monitors or a switch box, whether an RTG screen remains static or not depends on whether the Amiga mode takes over the system. So, WHDLoad will freeze the RTG output, whereas a multitasking-but-chipset-only program like DPaint won't. IE, I'll still see my DOpus clock ticking on the RTG Workbench screen if DPaint is up on the other monitor.
Keep Amiga Video will do the same for native screens, I think. So if your Workbench is NTSC and you run Photogenics on an RTG screen, your Workbench will remain visible and your clocks will keep ticking away. There's a chipmem access speed penalty, according to the CGX docs. Might be slightly different on P96.
Fake Native Modes is an attempt to do just that - create fake Amiga native screen modes if you don't have a way to display chipset video. It hasn't worked very well in my experience - no better than ModePro.
