When I was about 12 years old I used to watch my grandfather shave with his straight sometimes. He did not have running water, and had to heat the water on the wood stove they cooked on, and poured it into a large white granite coated pan used for washing and shaving. Once in a while he would get his stone out and sharpen and then strop the razor. He held the razor with two hands when sharpening, using the index finger of his left hand in the barbers notch of the razor to steady it on the hone. He told me that was what the notch was for. To keep his finger from slipping.
Just another story to add to the many others.