You might feel just fine with your camping pad, and many people do. A cot is another option to put something between you and the rocky ground. If you're comfortable sleeping directly on the dirt, scroll on, light packer!
What I love about the cap cot is: it does not matter how rocky the ground is because you do not notice it; and you have under-the-bed storage. I stuff my riding jacket and pants under my cot, along with all my packing flotsam: drybags, tent bag, sleeping bag stuff sack, etc. All hidden away under the bed.
There are a ton of camping cots on the market; choose one that has the features important to you. Do you need it on the wide side (better for a side sleeper)? Does it need to hold a lot of weight? Do you need it to pack up very small?
Mine is a Tri-Lite cot from Byer of Maine. It's rugged, comfortable and made in the USA. I have slept on it for a lot of weeks over a lot of years and it's been great.
Some people need to combine a cot with a sleeping pad, either for warmth or for comfort. I say, you do you! Be mindful of how much extra weight you're piling onto your motorcycle though.