I'm trying to figure out how switch work with and without QoS. Let say that I would like to enable QoS on 3750 in a way to speed up VoIP traffic. I enable priority queue, Q1, for VoIP traffic (Cos 5, DSCP 46). As you enable QoS (for egress) you have to deal with 4 queue (with 3750). For VoIP traffic no problem is on Priority Q1. But for all other traffic that supposed classified/marked to defualt to Cos=0 and DSCP=0 will be sent to Q2.
In term of performances and optimisation the fact I'm not using 2 queues (Q3, Q4) will mean that for non VoIP traffic I have performances/optimisation degradation vs the situation without QoS enabled ?