A septoplasty is a reshaping of the septum, the wall that separates the two sides of the nose. Its purpose is to improve breathing. While this can be responsible for breathing problems, in the past some plastic surgeons would do a small and insignificant septoplasty because in the past insurance companies would pay for septoplasties, but they never did for rhinoplasties.
So the septoplasty was effectively an excuse to get the rhinoplasty covered by insurance. Certainly there are a great many patients who in fact need septoplasties today, but because of the changes in the attitudes of insurers they are less frequently done than in the past.