I have a dual monitor setup with my workspace spanning both monitors.
I use various panoramic photos as desktop backgrounds.  Until the most
recent version, I could choose to center, scale, stretch, etc. and it
would work across both monitors.  I notice that someone else
considered that a bug :-), and now there is a separate "span" style.
But "span" is not an alternative to the other styles, it is
orthogonal.  It should be possible to combine "span" with any of the
other styles (perhaps as a checkbox item), so that one can get the
previous behavior if desired.