If you disconnect your second monitor, before moving the visible applications back to the primary monitor, Windows will continue to launch them off screen. And then you're in for a world of hurt, because it's not obvious how to get them back.
I don't know why Windows will launch applications off screen if there is no second monitor detected. Even worse, I don't know why they don't make it easy to get the application visible again. But they don't and here's how you do it:
- Use ALT+TAB to switch to the off-screen application.
- Press ALT-SPACE to launch the system menu (you won't see: it;s off screen)
- Press R to select the "Restore" menu option which ensures the windows isn't is maximized (a maximized app can't be moved)
- Press ALT-SPACE ,
- Press M to select the "Move" menu option.
- Press any arrow key to transfer focus
- Now just use the mouse to place the window where you want (or just hold down the arrow key to slowly bring it in to view)