Or to place a source within the sound stage. For instance to have a stereo piano on one side of the sound stage rather than spread unnaturally right across it, similarly with drums to avoid a kit being over-wide.
Using the balance panner will alter the balance of the L and R components within your stereo signal, whereas the combined panner will allow you to alter their placement without affecting their relative balance.
When mixing band material, I find a useful starting point is to visualise a little set of musicians who have set up their gear on my meter bridge just as they would on stage, then align the basic mix to their relative positions on that soundstage. The kit roughly central and occupying about a quarter to a third of the stage width, stero guitars toward the L and stereo keys toward the R, for instance