If running a factory 3" barrel with a S&W K/L snub, the 3" barrels allow for a full length extractor, providing for full extraction, while the 2.5" barrels have a shorter extractor/extraction of empty cases.
Trying to debate the difference between calling one or another revolver a "snub" or a "short-barreled" revolver is a trivial pursuit. In the days of service revolvers (when I started in LE), "duty" barrel lengths
mostly were taken to mean 4" - 6 1/2", and 2" - 2 1/2" were usually considered "snub" models.
The 3" S&W revolvers were usually considered akin to being a snub (close enough), but with the added advantages (over the 2 1/2" S&W's) of longer extraction/ejection, as well as a bit more barrel length to boost velocity.
The poor Ruger Security/Speed-Six owners were often left out in the cold, with their barrel lengths of 2 3/4", but us Ruger shooters considered them snubs, and shot the living daylights out of them.
Now, my M36 nickel 3" heavy barrel is still a "snub" in my mind, as were the pair or early production Charter Arms 3" .44 Bulldogs (suppressing a shudder remembering them) ... but their 3" lengths, like the larger framed 2 1/2" K's and Security/Speed-Sixes, made them more belt guns than pocket holster snub guns.