In my case I am now using a 13" M1 MBP but I previously used a 12.9" IPP in exactly this same way. I run my stock trading/monitoring app on the 13", same app I used on the IPP. Meanwhile, I do research, clip things to Notes, and other "general" tasks on my 16" MBP. I now can use one keyboard and mouse to interact with both. If I see something happening on my "summary page" in the stocks app, I can easily mouse over and click expanded view to see if I need to take some action. Generally I may already have my hand on the mouse so this is virtually just like having one system with 2 monitors. However unlike 2 monitors, if I decide to leave my desk, go to lunch, etc I just grab the 13" and I am good to go.