In the 'old days' they made 'balloon head' cases that is the rim was hollow and wouldn't take the higher pressures of the modern solid rim cases. The counter bore was to be a safety in case the rim ruptured .
Balloon cases are no longer made so it's a moot point !!
There is a certain amount of confusion about that.
There have been three types of centerfire cartridge, not two.
The "folded head" made like a rimfire but with centerfire priming - early ones internal so they even looked like a rimfire - was not strong and was subject to rim ruptures.
The "balloon head" has the characteristic primer pocket bulge into the powder space because the head is thin. But the rim is solid. UMC even headstamped such cases
S H for Solid Head. While at risk of casehead separation with heavy loads or reloads after mercuric primers, there is no particular danger of the rim rupturing. Sharpe referred to them as "semi-balloon head" but thought they should have been called "solid rim."
Now we have the standard "solid head" with the casehead thick enough to contain the primer pocket. Stout stuff. (You can look at some of the cheap 9mm empties and see some strange contours down in there, though.)
The first recessed rim revolver cylinders I know of were in .22s, about the time .22 High Velocity ammo came out.
The first recessed rim centerfire revolver cylinder I know of was the S&W .357 Magnum. The .357 Magnum was introduced in solid head cases and by that time, even semi-balloon head .38 Special was not common. So I don't know what S&W thought they were guarding against. Nothing that worried Colt or Ruger, at any rate.
Elmer Keith made a distinction between balloon head and solid head .44 Specials, loading the stronger but smaller volume solid head cases with a grain LESS of No 2400.
Henry Stebbins wrote in 1960 of finding most of a box of solid head .45 LC at the range, which he and Bert Shay thought a Fine Thing, but did not say when that actually occurred, he put a lot of history in that book.