VLAN tagging can minimize the cabling as well as the switch ports used, to integrate the endpoints in the current network while still separating the Voice network from the Data network. A workstation can be connected via the PC port on the IP phone in the default or different VLAN. You can apply priority options via the 3CX Console (and matching switch configuration) to the LAN/WAN port and/or PC port in order to instruct the switch to handle real time traffic, such as RTP (voice) over the normal network traffic.
Pros using IP phone switching and VLAN Tagging
Assuming a workstation is directly connected to a switch and you want to add an IP Phone, no extra switch port is required and the network resources needed are low. In this case, the workstation can be connected to the PC port of the IP Phone and the LAN/WAN port will be connected to the switch. The switch must be configured accordingly to allow multiple MAC addresses on one this port (if MAC filter is enabled). If the need arises to split VoIP and PC network from each other additional different VLAN/- priorities can be given to LAN/WAN and/or PC port. This is where the new VLAN provisioning method of 3CX comes into play.
Cons using IP phone switching and VLAN Tagging
Although using the switch port of the IP phone can eliminate additional hardware/cabling, in case the PC port is used to connect a workstation to the network, in other words, the IP Phone is used as a small switch, upon IP Phone reboot, the workstation is going to lose the IP address. Therefore, it will be isolated from the local network and as a result, any online services/applications will be dropped. In a similar scenario, a workstation connected directly to the PC port of an IP phone, with high bandwidth demand (high network traffic) will allocate additional hardware resources from the switch which, in this case, would be the IP Phone, therefore can lead to audio quality issues if not correctly handled with VLAN priorities and the vendor of the IP phone.
Read on how to setup VLAN Tagging for IP phones.