The MOAB dropped on Afghanistan

Does size matter when it comes to bombs? Generally, no. The media loves phrases like “carpet bombing” and “mother of all bombs.” Generally, bombs are rather mundane like a workman’s tools.
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The appropriate size bomb depends on the nature of the target. Also, different bombs have different fuzes and casings. The fuze determines where it blows up: in the air, when it hits the ground, or delayed until after it penetrates underground. Some casings stay intact to penetrate. Others are full of like big shotgun pellets to kill people in a wide radius.
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The size of the bomb is determined by the size of the target and/or how hardened it is. For example, you carpet bomb a carpet-shaped target (that is done by a line of bombers flying wing tip to wing tip and dropping their bombs simultaneously).
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Our enemy in Vietnam was big on tunnels. They were extremely effective as protection from our tactical fighter bombers. When our infantry found a tunnel, the had trouble destroying it with C-4 explosive. Was there an effective weapon against the tunnels?
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Yes. The B-52. That is a very heavy high altitude strategic bomber. It drops relatively big bombs: 750 and 1,000 pounds. The attacks were called Arc Light Strikes. I experienced on once—from 20 miles away. We neither saw nor heard the bombs or the explosions. But the buildings where we were shook violently and audibly like once every eight seconds for about three minutes.
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Imagine being on the receiving end. In fact, the Arc Lights crushed the enemy in those otherwise invulnerable tunnels. Because the B-52 flew at 50,000 feet, the first indication there was an attack was bombs exploding. When they were first used in Hanoi, our POWs said their guards were visibly shaken. When the NVA masses around Khe Sanh. We hit them with B-52. Here is a quote describing the effect on the enemy:
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Many enemy casualties were due to concussion alone. In some instances, NVA soldiers were found after an Arc Light strike wandering around in a daze, blood streaming from their noses and mouths. To catch these stunned survivors, artillerymen at Khe Sanh often brought massed artillery fire down onto the Arc Light target area 10 to 15 minutes after the heavy bombers departed.
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Here is an enemy account of being on the receiving end of such huge bombs:
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In the jungle, life's conspicuous features were the same for everyone. We lived like hunted animals, an existence that demanded constant physical and mental alertness.

Of all the privations and hardships, nothing the guerrillas had to endure compared with the stark terror of the B-52 bombardments. Bombs of all sizes and types were disgorged by these high-altitude predators, which were invisible to us on the ground. The statistics convey some sense of the concentrated firepower that was unleashed on both North and South--more than three times the tonnage dropped by the U.S. in World War II. From our perspective, these figures translated into an experience of undiluted psychological terror day after day over years.

From half a mile away, the roar of the explosions tore eardrums, leaving many of the jungle dwellers permanently deaf. The shock waves knocked their victims senseless. Any hit within a quarter of a mile would collapse the walls of an unreinforced bunker, burying alive the people cowering inside.

The bomb craters were gigantic, 30 feet across and nearly as deep.

It was something of a miracle that from 1968 through 1970 the attacks, though they caused significant casualties generally, did not kill a single military or civilian leader in the headquarters complexes. This luck, though, had a lot to do, too, with accurate advance warning of the raids, which allowed us to move out of the way, or to take refuge in our bunkers, before the bombs began to rain down.

B-52's from Okinawa and Guam would be picked up by Soviet intelligence trawlers in the South China Sea.

Often the warnings would give us time to grab some rice and escape on foot or bike down an emergency route. Hours later we would return to find, as happened on several occasions, that there was nothing left.

It was as if an enormous scythe had swept the jungle, felling giant trees like grass, shredding them into billions of scattered splinters. On these occasions the complex would be utterly destroyed: food, clothes, supplies, documents, everything.

It was not just that things were destroyed; in some awesome way they had ceased to exist. You would come back to where your lean-to and bunker had been, your home, and there would simply be nothing there, just an unrecognizable landscape gouged by immense craters.

Equally as often, though, we were not so fortunate, and had time only to take cover as best we could. The first few times I experienced a B-52 attack it seemed, as I strained to press myself into the bunker floor, that I had been caught in the Apocalypse. The terror was complete. One lost control of bodily functions as the mind screamed futile orders to get out.

On one occasion a Soviet delegation was visiting our ministry when an attack began with especially short notice. No one was hurt, but the entire delegation sustained considerable damage to its amour--uncontrollable trembling and wet pants the all-too-obvious outward signs of inner convulsions.

The visitors could have spared themselves their embarrassment; each of their hosts was a veteran of the same symptoms.

Eventually, though, the shock of the bombardments wore off, giving way to a sense of abject fatalism. The veterans would no longer scrabble at the bunker floors convulsed with fear. Instead, people just resigned themselves— fully prepared to "go and sit in the ancestors' corner."

The B-52's somehow put life in order. Many of those who survived the attacks found that afterward they were capable of viewing life from a more serene and philosophical perspective. It was a lesson that remained with me, as it did with many others, and helped me compose myself for death on more than one future occasion.
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The recent MOAB target in Afghanistan was, in addition to 36 bad guys, tunnels and bunkers the IS guys used to hide from US bombs. They don’t work against 750 and 1,000 pound bombs, let alone 22,000 pound bombs. When they used the much smaller, but still huge, daisy cutters in Vietnam and Desert storm, they found dead enemy some distance from ground zero without a mark on them. Some sort of asphyxiation from the explosion taking all the oxygen.
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In short, when a bomb goes about the 500-pound level, I am not sure what all those people who say you can’t win with airpower alone are talking about. Ground zero bears no resemblance to planet earth. Humans there were vaporized or blown to bits or squashed flat in a tunnel.
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A little farther out, they are dead, for no apparent reason. A little father out, the are permanently deaf, maybe permanently shaking with permanent PTSD. In the kill and permanently disabled zones, you sure as hell can CAN with air power alone. When it’s 22,000 pound bombs, the war is over for the enemy within a mile of more.
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So a huge bomb is not just a bigger version of a regular bomb. It is a game changer.