Copy on the fly

Hey i have tried copy on the fly using a dvd in nero 6. Everything works ok and comes out with a solid product. Im was just wondering if the device buffer going down to 18% and then back up and down fluctuating and read buffer is 50% is going to leave sskips or puase or just lower quility burns? But after about half way throught the burns both buffers fill up all the way and stay filled. whys this?