When I did a defensive pistol course we were taught to slightly rotate the pistol when shooting with one hand. It was explained that it was a more natural position for the hand / wrist. Thats not to say it was completly sideways but I could see where there could be benefits to it.
I too learned this, but only when shooting weak hand only (Or is it called support hand these days? ) With my left arm straight out in what could be called a one handed isosceles stance I have to cant the weapon a very slight bit to utilize my dominant eye.