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.
The current behavior is based on GIMP, Inkscape and MyPaint, which all scroll when spacebar is held, without needing to click. Also, I don’t think I can start changing keyboard focus based on where the mouse pointer is without causing some serious usability issues for many users, because that would be very unexpected.
That said, I can see how some people may prefer to click while panning, so maybe there could be some option for this. It would likely not remove the need to focus the map view before pressing space though, simply because space can mean something else when the focus is elsewhere. Like typing an actual space, or to toggle the visibility of the current layer in the layer view (worked in Tiled 1.0, fix pending for Tiled 1.1.4).
To focus the map view without making any changes, you can use middle click. Of course, middle clicking allows you to pan as well…