And sound, every inch in a shotgun significantly reduces report.
The difference between an 18" and a 26" barrel for example is great.
The large bore means each inch of length results in a lot more space for compressed gas to expand into which reduces the pressure it finaly escapes the muzzle at.
A single inch of .729 bore gives 1.67 additional cubic inches of space.
Compare that to a ~.30 inch rifle bore that would need almost 6" inches of barrel to create that much space.
This means an additional 2 inches of unchoked 12 gauge bore is giving as much additional internal space for gas to expand into as nearly a foot of a .30 caliber rifle barrel.
Or lets compare to popular .223/5.56 (actual bore is around .224), where it would take about 10.6 inches of barrel to give the internal space of a single inch of 12 gauge. And an additional 2 inches of 12 gauge barrel is giving over 21 inches of .223 rifle bore space.
And the difference of the 8" of bore space between an 18" and a 26" barrel would be 13.36 cubic inches the amount of space in over 84" of .223/5.56 barrel. So it has as much extra internal space as an extra 7 feet of .223 barrel.
The whole 26" barrel would have around 43.43 cubic inches. Or as much internal space as 275" or nearly 23 feet of .224 barrel.
Which starts to seem a lot more signficant in those terms, and you can see why just a few inches in 12 gauge makes such a difference in reducing the volume of the report.
Being relatively fast burning and operating at low maximum pressure with a large bore volume most shotgun powders have completely burned before getting anywhere near the muzzle. So that additional volume for gas to expand continues to drop pressure and report volume.
Decibels are in a logarithmic scale, so the difference between 150 and 160 decibels for example is a lot more than the seemingly minor numerical difference of 10.
This can mean the difference of being nearly deaf for awhile after firing indoors and simply having reduced hearing.
That doesn't mean increased length outweighs how handy and convenient a shorter barrel is maneuvering in confined spaces, only that it was an unmentioned benefit of a longer barrel when weighing pros and cons.