Area denial, meant to irradiate large areas of land incase of war, back when the thinking was in a nuclear war up to 400 warheads a day would be used by either side instead of the more recent thinking of "mutual destruction".
So you have a enemy column moving in on you? Don't have the manpower in Europe to actually stop them? Just launch one of these bad boys in their column to stop them where they are.
The biggest problem at the time for this weapon was it gave the power to launch nuclear weapons to "lower ranks" (mainly Sgts in charged of the units), which was why it got canned.
Dimitri