I would suspect that the vast majority of such hauls is drug money laundering related. "Normal" folks would be scared of losing such cash or having it stolen. I know I would be petrified at the thought.
However, there are probably a few folks who don't use banks (don't trust 'em or don't use 'em just because) and this is how they buy a house or buy a car or go from one state to another with their possessions.
Now, here's where my ambivalence comes from: do we let the money laundering go because a few of these are false positives? Or do we accept the false positives because it serves the greater good because it catches or causes attrition for money launderers?
I think electronic or check transfers are a rational solution to the problem at hand and so folks should use that.
But I'm still ambivalent. Constitution. Checks and balances.