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
Gripping the the pistol canted was a suggested
technique by my instructors when shooting with only the "weak" hand. This optional method actually did seem to help me a little.