Guarantee of Service, GoS, provides control and predictability. Without GoS, packets are free to run randomly which results in jittery voice, slideshow style video, and out of sync collaboration sessions. While fatter pipes may mask the problem temporarily only GoS can fix the problem. GoS is more granular, efficient, scalable, and easier to configure than any other approach to QoS.
It's time to get real, it's time to get GoS.