While I own both C/P and disc drag reels I set the tension just enough to prevent over travel (backlash) when I strip line while fishing or casting. If I hook a big fish that requires more braking to slow or turn it it has never entered my mind at the time to adjust the drag with a fish on. The excitement of the moment does not lend itself to trying to turn a drag knob.
There are built in drags from friction of the line thru the guides or even the water itself or the weight of the line which make a fish work harder...and I can palm the rim or apply pressure as the line passes thru my hand.
My point is disc drags are not only not necessary but they add weight and increases the price as well.