If you picture a cam lobe with flat flanks leading to the nose, and then imagine that same flank wit ha point on it where the flank itself would look like it has an a point where the lifter actually looses lift (IIRC the lifter literally doesn't lose lift at that point but the inverse radius basically stalls the lift rate.
That's the only way I can explain it. Rather than a flat flank, the flank has a dip in it, for lack of a better term.
As to why it is better, I'm not sure. I do know there are cases where it works. What parameters those may be I can't say.
