VLAN allows you to create a virtual switch within a switch! So assuming you are working with a 24 port switch. You can configure ports 1 - 10 ports to be on VLAN1 (192.168.1.0/24), and ports 11-20 ports to be on VLAN2 (192.168.2.0/24).
So it’s like you have partitioned your switch into two, and now your network looks simpler!
You can combine your dual NICs machines and potentially reduce the latency, and/or double the bandwidth (Not supported with Ubiquiti Unfi).
Isolate any noise between the NAS and the music streamer.
This can be daunting if you have never configure a switch before.
Like #1, devices on VLAN1 cannot communicate with VLAN2 (a router does not exist in this diagram).