The need for bass is not always the largest places, but rather, the rooms that are the hardest to cover. I use it if I play for younger dancers, or do a lot of DJing during a show....like a Bar Mitzvah where I am switching between kids stuff and classic stuff all night.
The new G2 10s are just as powerfull as the old Gray 15s, so I doubt that I'd need more than one sub and two tops for anything I do. In case of an outdoor thing, or where 4 way coverage is required .... I have a second pair of the gray ones (15). They will sit silent most of the time, though !