A lot of Sellers will point this out as a way of alerting you to the fact that the gun is of older vintage. Similar to the terms 5 screw, pre model or diamond stocks. All of these "terms" alert collectors to time frame distinctions that tend to make the piece more desireable.
As an example, pre models are generally before 1957 when the Govment required all firearms to be model marked, diamond stocks are those made before about 1968 when S&W stopped putting the unchecked diamond around the stock screw. Pinned barrels and recessed cylinders were discontinued about 1982 except for the 22's. I hope that helps.