Originally Posted by Grigori

...Remember that every time the standard rotation refreshes its diseases, it effectively loses 4-sec worth of diease damage (2 sec loss for 2 diseases) because its disease refreshes are two rune sets apart. Effectively, the standard rotation only has 18 sec disease uptime every 20 sec.

Now, the SS glyph rotation refreshes diseases roughly 1.6 times as often (if I remember correctly). However, almost all of the refreshes are either near-zero-loss or 2-sec loss; very few refreshes incur a 4-sec loss that the standard rotation refreshes incur. This results in a net gain in disease damage...