Pictured above is the upper level of the engine terminal staging elevator prior to operations many, many months ago (there have, unfortunately, been no ops since!) . There are eleven locomotives squeezed in place. This is obviously the maximum amount for staging. However the lower level, which contains the terminal service trains (coal, ash, etc.), has plenty of extra trackage where some more locomotives can be staged.
In practice, though, the lower level is typically used to get traffic off the layout in an emergency. This usually means that the elevator is up to let off/take on a service train while at the same time a road engine needs to go from the ready tracks to the station platforms (i.e. staging). The Staging Master can “bail-out” the road locomotive while the whole contraption is up, saving him some cranking.