I'm admin of a LAN and now I'm supposed to configure routing on it.
I can define some VLANs on the network and also configure inter-VLAN routing between them(by SVIs or router on a stick). But when I associate each VLAN a subnet, what is the necessity of defining VLANs? Without VLANs, there are some subnets and I configure standard routing, like OSPF, between them and subnets, are separated from each other(like VLANs). So I can't recognize whether to use VLAN-based design or another. Could you please help me with this?
I don't understand your question to be honest. If you need separate subnets, you either use SVIs (VLAN interfaces), or physical (sub) interfaces, as you have mentioned. If all are configured on the same device, you don't need any routing protocol.
What does your network look like ?
can you add a picture of your network including subnets. if you have a faitrly flat network, you might get away with intervlan routing. cheers