VLAN-Groups Self IP Assignment vs. Supernet

Hello all. I am struggling to understand two things regarding VLAN groups. The documentation provides two possible use cases:

1. Grouping multiple VLANs into a container so the servers within member vlans see themselves rather within one VLAN

    

2. Allow client and server to communicate when they are on the same IP range

    

So I've got a issues regarding each of the scenarios above:

Q1: If one VLAN 10 uses 10.1.2.0 /24 and VLAN 20 uses 10.12.3.0 /24, what would the VLAN-Group self IP would be? My understanding is that the IP address & mask should include both VLANs above! Does this then mean I need to super net the two? This could be tricky in some scenarios where discontiguous networks are being used?

Q2: What would be a realistic use case of the second scenario??

thank you so much.