Layer 3 segmentation without vlans!

Hi Guys,

So I'm trying to get away with not setting up vlans on a switch. I know that in the past the IP address of the vlan doesn't matter to the client systems. For example if my layer 3 switch has vlan 10 with IP of 192.168.255.254/24 I can still hook up two client systems on a 10.10.10.0/24 network and the client systems can communicate with themselves, albeit not with the layer 3 portion of the switch, but layer two seems to pass the traffic just fine between the two separate networks - without vlan segmentation.

I know everybody will say create a vlan for my below senario, but I'd like to understand if it's really necessary or just a best practice to isolate the networks on the layer 2 side? Like do I really have to create an addtional vlan If I want to run two separate networks on the same switch... if so why? Because it seems to work fine with only one vlan.

Here are the links to diagrams :

https://ibb.co/fC62CNg

https://ibb.co/wyP5y6f

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Best,

Mud

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P.S. if you are really curious about why I'm using both 10gig link and 1 gig link on the iMac Pro computers it's because the AVID ISIS server doesn't support the iMac Pro 10gig ports, but the FreeNAS does.