Hi Roger, your "useless" comment is related to earthquake short-term prediction. But, knowing whether and how quakes are clustered is interesting for other reasons. If quakes are being triggered by distant quakes, or there are cycles of global seismicity (for totally unknown reasons), that is interesting to me just for its own sake. But, this could also shed some light on how quakes initiate which in the future could allow some progress, however small, in prediction.
Chris