All it provides is an additional light source, nothing more, nothing less.  As I stated above, the workload of the lighting is achieved from the HDR Background.  The Bestep setup that Rhia mentions in her post makes the HDR Background easily rotatable even though it incorporates the same nodes as the Setup Scenes.  I disagree with using the Gamma node to control intensity output, it distorts color output at higher values, but I found a solution for that.