Back in the early days of CD burning, burning at high speeds would sometimes result in the buffer becoming empty and having to wait a slight second for it to fill up with more data, to be written to the disk.
Referred to as "Buffer under run"
As a result, you would get a jitter effect on the cd or dvd.
Back then it was highly recommended, espescially when burning ISO files, that you burnt at lower speeds to counteract the problem, and end up with an error free burn.
These days all of our burning software contains code to never allow the buffer to run empty, therefore we rarely have any problems in that area anymore.
It keeps the buffer constantly filled with data, therefore avoiding the buffer underrun problems of the past.
I always burn at Maximum speeds these days, and never have any dramas.
I hope that gives you a plausible answer
