Since disposables are lighter than DE razors there is a tendency (at least for me) to press harder which resulted in hairs being cut below the skin & causing folliculitis, i.e., ingrown hairs. Multiple blades easily compound that problem. I have always believed that multiple blade heads were merely a gimmick as Gillette was feeling the heat in 1971 when Bic introduced the first disposable. Gillette, which had come out with the Trac II in '71 as well, used the same double blade concept in their first disposable in '75, the Good News. It has been a game of "one upmanship" ever since.
Surely, Gillette has done a superb job of conning the public into believing that multi-blade razors are a necessity whereas we have yet to see multi-blade steak knives or bayonets.