@dengelhardt that's a good point that people often miss - there are cases where using VLANs unnecessarily can cause traffic to have to "loop" through a router to return to the same device. In the case of VoIP phones acting as small switches at the desk it's the switch inside the phone doing it.
I had to deal with a network just a few weeks ago that had five routers and three switches, one of which was still on FastEthernet (10/100.)
They managed to make nearly all traffic have to pass through the slow switch for nearly everything. And some things looped through routers that were attached on both ends to the same VLAN!! It was insane.