Myth of burning slower. Discs are made to perform at an ideal rotational speed, which is where write strategy originates. The disc will perform best up to a certain speed, and the drive will not permit any faster. The inverse is the same, but until recently, drives would not prevent unreasonably low speeds. Modern human nature tends to want more speed and more power, so this was not really a concern.
But believe it or not, there are still people who insist on waiting 55-60 minutes to burn a CD or DVD at 1x speed, because they are convinced anything faster will yield a bad or "lower" quality burn. However, burning too slow is often just as bad as burning too fast. Because of this unreasonable impulse to go too slow, some discs and drives now block out the lower range too (and causes problems, see the 16x section for more).
There was some truth to that statement in the beginning, (circa 1995 for CD-R, 2001 for DVD-R), but those days are long gone. The only reason that myth ever held truth was because 2x was the fastest speed, and burning a single full or half speed under the maximum rating is helpful on lower quality blank CD/DVD media. If you are worried about quality, or if the media tends to be dodgy quality at the maximum rated speed, then burn a full or half step slower. No more. With a 8x disc, for example, a burn speed of 4x or 6x would be optimal.