Yes, that is correct Eggz. The best example I can think of is if I wanted to make a stained glass window but instead of using the tile generator I wanted to supply my own mask and have SD "read" that each white area is different. This way I could apply either gradients or solid colors to each pane of glass.
Another example would be if I wanted to make a brick generator that I could always feed a black and white mask into so that I could get some really crazy shapes easily. Having something like what I've asked for in this thread would allow me to give each brick different depths, colors, or slopes because SD would now recognize them as individual shapes.