Wired Intelligent Edge

What is really the difference if I tag a Vlan as voice or if I dont then give the vlan a high QOS? Is there really any advantage in setting the vlan to phone rather than data if the vlan links are separated? 

A voice tagged VLAN will probably be communicated via LLDP-MED to the phones as well.

For what it's worth - the HP Press AIS Network Infrastructure exam prep book advises that Voice VLANs "separate, prioritize, and authenticate voice traffic moving through your network, and ... avoid the possibility of broadcast storms affecting VoIP (Voice-over-IP) operation."