The data rate is likely to be the limiting factor
No, it's going to be the amount of processing power you've got. In the future you could put more up there but that has problems. You could also put more lasers on the satellite and have more bandwidth.
What you can't do is make light go faster. On-satellite analysis could be critical if you wanted to run a fairly simple algorithm on a fairly limited amount of data and detect a fairly obvious feature very quickly, and do something automated with that information right away in orbit, or at least on that side of the planet. Like detecting blooms on thermal imaging. For example.
There is no "oh, natural disasters and stuff" application where it's not more efficient to return the images to the surface. There also aren't any such applications where you wouldn't want to have the images available to view.