As others note, it is personal preference and it also varies according to where I'm going. Note that we don't fish, so this is purely for navigation and situational awareness.
Most commonly I keep the left screen in split-screen mode showing radar or sonar plus a zoomed-out longer range chart. That screen is for general orientation and collision avoidance. I also use it to check guages, etc, when needed. And to do routing for the automatic course line. It is quite possible to show 3 sections (e.g. chart, sonar, and guages) but I prefer the 2-panel layouts.
Then I keep the right hand display on a full screen chart, which is zoomed in to show local, finer detail for immediate navigation.
Overall we love the dual displays!