My understanding of VLAN must be flawed because it's not making any sense to me and seems redundant.
So lets say I have two IP ranges: 192.168.0.1-192.168.0.254 with subnet 255.255.255.0 192.168.1.1-192.168.1.254 with subnet 255.255.255.0
Now, from these two ranges, a single router is used. Each IP range is on a separate LAN port of the router. I am asserting that these are two completely separate broadcast domains because the routing table has entries between these two IP ranges to allow routes between them (if I remove or disable these entries then they are unable to communicate). [If my assertion here is wrong please let me know].
Assuming the above is correct, now enter two VLANs VLAN1 and VLAN2. Now, my understanding is that a VLAN creates two or more broadcast domains. So in my mind I would configure VLAN1 on 192.168.0.0 and VLAN2 on 192.168.1.0 but isn't that just redundant since these two IP ranges are already separate broadcast domains? So why would I choose to VLAN tag them? What am I not understanding?