I do back and front cuts myself, not hard. 15 degrees seems to be the consensus. Some engines benefit more than others, some don't at all. Some valves have more to cut on the back side than others. The end result is more flow at lower valve openings, i.e. the air gap is greater at a certain lift. But the "ramp" you are supposed to back cut, also directs mixture to the side, and if you remove it, some combustion chambers don't like it. I have read numbers like 10% more flow, but not in every engine. That's the best case scenario.
