Getting a bit too technical for me now Jon.
Say, just for example, your intake port flows 200cfm of air at 0.5" valve lift.
If your valve only just reaches that height at max lift it is only going to flow that much for a tiny fraction of a second. The rest of the time it will flow a lot less.
But it you could open that valve faster you can hold it at that lift for longer before it needs to close again. Therefore get more air and fuel in.
There is also a benifit from opening the valve mush more than you need for max flow. This is because you then increase the
average time that the head flows at max.
The air/fuel mixture is actually quite heavy. At least it behaves that way in an intake runner. It has inertia. So it is hard to get it going but also hard to stop.
If you get a big flow of air/fuel going into the head then you can still get something near the max flow happening even after the valve has closes some. The "RAM" effect. So getting that air moving well is vital to filling that cylinder with a decent pressure of mixture.