I don't think the pinned barrel and recessed (counterbored, really) chambers have any practical advantage. They are more a call back to the "they don't make 'em like they used to" traditionalist point of view, which is understandable when collecting artifacts of historical interest like S&W.
I do not like the counterbored chambers because they do tend to trap more gunk. I have shot C'bored revolvers that, with even a small amount of dirt in the "recess," would cause the cartridge heads to drag on the back of the frame. I never have had that problem with "non"-C'bored chambers that were less likely to trap dirt.
I think the C'bored chambers were originally a safety nod to the old folded, or "balloon" head cases, which could rupture. I do not know if the magnum ammo was ever produced with balloon-head cases, but the modern solid-head cases have made that concern obsolete. The .22 caliber rimfire revolvers still use C'bored chambers because .22 rimfires do use folded heads.
As for the pinned barrel, I don't know when in Smith's engineering history the "pin" appeared, but it could have been a necessity of older manufacturing technology that was carried forward. This is just a guess; I defer to forum members who are much more knowledgeable than me.
It seems to me that Colt has always done fine without the "pinned and recessed" features.