VLAN (Virtual Local Area Network) is used to create multiple virtual LANs on a single physical interface. It is a layer 2 method that divides a single broadcast domain into multiple broadcast domains. So, proper VLAN planning can increase your network performance as well as network privacy.
There are various situations when you need to create VLAN in your MikroTik router. For example, if your ISP provides your WAN connection through a VLAN, you have to create a VLAN on your WAN interface or if you need to isolate your VIP users from other network users for any security purpose, VALN will be a better solution to isolate your physical network into multiple logical networks.