Both cause the creation of uneven edges. If I grind down on the middle of the skate blade I will always produce even edges. When skating aggressively, particularly in hockey, the inside edge is worn off more than the outside. Furthermore, the inside edge is worn mostly under the ball of the foot and not much at all near the tail of the skate blade. Look at Figure H .
All illustrations are exaggerated for effect.
Here we have a skate with a high top edge coming into the grinding wheel. Note that the initial touch or first pass will only show grinding marks at the top of this skate. Again if you lightly touched the tip and tail of this skate to the wheel, or took one light pass, you will see that you are only grinding at the top of this skate. This is NOT an indication of where you will end up. This is only showing the wear pattern on the skate blade.