I know that the specific case I mentioned has been fairly useful in fighting money laundering and large-scale drug-dealing, though. There's something to be said for making it hard to move large amounts of money through banks without being observed, but as always there's no good way to do that without interfering with legitimate commerce.

As far as I know, the floor is defined by either "this would be too inconvenient even for money launderers" or "the false positive rate is too high to pursue this more strictly".