When you hold down the SPACE bar, you can drag the map around, but if the map window doesn’t have focus, nothing happens, and depending on what tool selected, sometimes destructive things can happen. It would be nice if the SPACE bar worked based on what window the cursor was over, rather than who had focus. I also struggle to give the map window focus as clicking on the map will often stamp a tile that needs to be undone.
This is more of a personal preference based on using Photoshop all day long, but the SPACE bar works a little different from PS. In PS you have to drag the window while the space bar is down, but in Tiled, you just move the mouse. Since I am accustomed to clicking/dragging, there is where I often have to UNDO changed if the window doesn’t have focus.