You said carbon fiber, but I think there is a fair chance you didn't mean carbon fiber. Maybe you just meant fiber, because that seems to be what you've spoken of.
Fiber is just that, usually red in color, done with the old Champion tips, as well as the latter Triumph tips. Also, earlier Crown tips had black fiber pads.
Also, red fiber pads are placed below just about any tip by a lot of cue repairmen, whether single layer, or layered. Some do it for the look, to be old-fashioned.
Carbon fiber, on the other hand, much harder, believe OB was the first, but maybe somebody preceded them. Pretty close to dark brown or black in color for the pad. Totally different from fiber.
If glued with expertise, with no gaps, minimal difference, though some may say they detect some difference. But their shooting hand is a few feet away.
With an ivory ferrule, not a bad idea to have a fiber pad, if for nothing else, to remind you to change the tip before it gets so thin that it cracks the ferrule.
With the carbon fiber pads, it's apparently such an integral part of the shaft, that it voids the warranty if you shave down a major portion of it. I wonder if they get out the micrometer to see if you've shaved down so much of the pad that the warranty is null and void. Personally, a warranty on a $200 dollar item to me is like a health insurance plan for a hamster, but your mileage may vary.
So, there you have it in a nutshell. To do the pad, or not do the pad.
Me? I do a fiber pad underneath a Triangle tip, on Mezz shafts. I like it all the way around. May or may not work for you. But, work it, don't just talk about it. Experiment.
All the best,
WW