#4B v. 00B
At the front of my career, ('79) my agency had adopted #4B, so had a number of other Federal agencies as well. The argument was indeed higher pellet count, thus denser patterns, and to a certain degree, higher hit/wounding rate. I have a 1965 or so dated article from the "Rifleman" that was endorsing #4B in combat use in Vietnam, using the same logic.
All well and good at bedroom ranges. But afield, when the shotgun got deployed for an LE incident, or certainly in a combat zone, one would think, the ranges are longer. or have good potential to be longer.
There the #4B pellet runs out of steam due to its smaller mass. The lighter #4B does not do so well on obstacles either (nor does 00B for that matter). Auto glass, sheet metal, even simple interior doors are a formidable barrier. For those reasons, many of my acquaintance carried slugs as a duty load in their shotgun, untill the advent of the patrol carbine as a regular item became a reality.
Finally, after about a decade, 1990', the agency went back to 00B. That, I think, is a national trend. For all that, one of the two shotguns here at bamahouse in the ready mode is indeed loaded with #4B. Intended for marauding coyotes at night, it would be bad news for human threat as well, within its limited range.