Appearance-wise, the recessed cylinders allowed the rear of the cylinder to mate up closely with the recoil shield. You will only see a fine line there. The round of ammo is fully enclosed, and the rims of the cartridges are barely visible. In short, it's elegant and well-finished
. If a .357 "balloon head" round from the old days is fired in a recessed chamber, there is better protection against the case giving way. As for the pinned barrel, there is no cosmetic advantage, but it's insurance that the barrel has not been twisted and remains at its original clocked position.
"P&R" guns come from the good old days when parts were forged and hand-fitted to perfection. S&W had a stringent quality control department in those days, too. Modern-day guns are slung together from MIM parts with little if any attention to fitting. Their main advantage is that it costs S&W less to make them, and the company profit is therefore higher.
In short, the P&R guns look more elegant and are visible evidence that you are getting a gun that was made and fitted right. Traditional purists (such as myself and many others here) think that the traditional ways of making things resulted in a superior product, engendering pride of ownership.
By the same token, I prefer not to use a P&R gun for personal protection, in case it winds up being thrown in an evidence bin following a potential fracas. They're just too nice to be treated cavalierly!