Howdy
I have no opinion on the effectiveness of the 32 S&W Long as a defense cartridge, because despite my extensive pistol collection, I actually do not carry.
But perhaps I can help with the historical aspect.
First, let's look at the ancestor to the 32 S&W Long, the 32 S&W.
The 32 S&W (sometimes erroneously called 32 S&W Short) was developed by the Union Metallic Cartridge Company as a Black Powder cartridge in 1878 for Smith and Wesson's little Top Break 32 Single Action revolver, which was also introduced in 1878. This example of the 32 Single Action shipped in 1889.
This little revolver was a five shooter.
The 32 S&W cartridge was very popular in the little Safety Hammerless revolvers (sometimes known as lemon squeezers because the grip safety had to be compressed to pull the trigger). This little five shooter shipped in 1905.
The 32 S&W Long cartridge was introduced in 1896 with Smith & Wesson's first revolver with a cylinder that swung out to the side, the 32 Hand Ejector 1st Model, sometimes known as the Model of 1896. Pictured with this Model of 1896, which shipped in 1899, are six rounds of 32 S&W Long on the left and six rounds of 32 Colt New Police on the right. The two cartridges were identical, only varying by about 2 grains of bullet weight, and the Colt rounds had a flat nosed bullet.
Here is a photo comparing the 32 Colt New Police round to the 32 S&W Long. Note the slightly different bullet shape, and the 2 grain difference in bullet weights.
This is probably the time to mention that in 1896, while he was police commissioner of New York City, Theodore Roosevelt selected the 32 Colt New Police revolver as the first standard issue revolver for New York Police Officers. Prior to that time there were no standard issue revolvers for NYC cops, they supplied whatever they wanted.
Sorry, I do not own a 32 Colt New Police revolver, but this little Colt 32 Police Positive shipped in 1917.
Not to be outdone in the law enforcement market, Smith and Wesson introduced their I frame 32 Regulation Police, chambered for 32 S&W Long, in 1917. This one shipped in 1924.
To illustrate the relative size of a 32 Regulation Police, this photo shows one under a standard K frame 38 Military and Police. Clearly the I frame 32 was more easily concealed than a K frame revolver.
I would be remiss if I did not brag a little bit and show my K frame K-32 Masterpiece, which shipped in 1954.
Getting back to the cartridges, here is some data I lifted directly from Wikipedia. I cannot verify how correct it is.
32 S&W:
85 grain lead, 705, fps, 93 ft lbs
98 grain lead, 705 fps, 115 ft lbs
38 S&W Long:
98 grain lead, 718 fps, 112 ft lbs
90 grain lead, 765 fps 117 ft lbs
85 grain lead, 723 fps, 99 ft lbs
So to conclude, clearly early in the 20th Century, the 32 S&W Long cartridge was felt by some law enforcement agencies to be suitable for a police revolver.