Well, I had said I'd try to keep this series positive but every now and then you run up against a problem.
It turns out Windows 10 is fairly terrible at remembering window sizes and placement when connecting to or disconnecting from an external display. So far I've had issues going both ways and having to rearrange all of my windows each time. On the Mac, it always remembers how I like my windows arranged in each context. I'm connected to an external display most of the time so I only feel this pain a few times per week.
This turns out to be a particularly frustrating issue if an app, like DropIt, doesn't have a Taskbar item. It means you can't "get a window back" onto the primary display without some sort of trickery.
Here is what you do: select the app by clicking on the primary icon for it, type Alt then Space then M (not at the same time) and that will allow you to move the "lost" window with your arrow keys to get it back.