The cam does this by making the ramp steeper. Too steep for a flat tappet lifter to maintain contact.
The value of faster opening and closing of valves is increased torque due to greater port velocity. There was always a lot of incense in the room when he spoke so I was always very lightheaded. That makes it hard now to remember what he said, so cut me some slack here. After all it was the '60s.
The problem with opening and closing rates is that you can over do it very quickly. What happens is that the valves start to slam on their seats. Too much slamming and well...no good.
Of course now these are good new days and the main reason to go to a roller lifter is eliminate the need for ZDT so that your catalitic converter will last 100,000 miles.
There is also this benefit of another .1 mile per gallon of gas. It helps manufacturers fleet averages when they sell a gabillion cars a year.
I think also that one can pick up another couple of degrees of effective duration.
On an all out comp car with big sponser bucks the roller was always the way to go. On a street car that is very unlikely to go 8,500 rpms, except if DT drives it, you aren't really going to see your extra 10hp.
I say keep it simple. Go flat tappet. It's way cheaper and will last a lot longer. I wouldn't drive one of these aftermarket roller setups further then around the block.
The sound of a broken valve train with a roller set up has a terribly expensive schrill and the flat bed might be busy that night.
But it's yo' money to throw away as you see fit. Enjoy.
