IPSC classified shooters into competition groups by power factor. At most matches this was done by firing at a steel plate on a pivot, and measuring the arc of movement. How far it moved, placed a shooter into major or minor category for competition.
For the most part 45s were major caliber, as were .357 for revolver shooters, while almost all 9mm loads and .38 were minor caliber.
Minor caliber allowed shooters to fire a course faster and therefore perceived at shooting at an advantage due to less recoil and quicker time back on target.
The 356TSW was introduced as a way to make the "9mm" a major caliber.
As noted, it did not really catch on.
