Basically the sweet spot is because nuclear explosions, for that matter all explosions, are spheres. So to double the radius it takes 8 times more “oomph.” So a big bomb like the 100MT Tzar Bomba could be replaced by 16 × 1.2 megaton bombs and blow up the same area of ground, without blowing up the 20 cubic miles of air above the ground at the same time. It would also use about 1/4 the fissionable material to produce the 16 bombs as opposed to the one big one.

We are basically being cheapskates with nukes. Yay! I see No PoTeNtIaL iSsUeS aRiSiNg" directly because of this.