Hey All. Hoping to gain a better understanding on transit VLAN’s in production...

I’m fairly new to the networking arena and I’m having a bit of a tough time understanding why I’m seeing many networks that have a connection between a L3 switch and a firewall with a transit VLAN on both sides.

When I think of the purpose of VLAN’s I think of segmentation and I think of two switches trunked together adding and removing tags. So I’m not sure why we use VLAN’s instead of just regular L3 point-to-point interfaces when connecting a L3 switch and a firewall. If we have a L3 switch, why not just turn the port connecting directly to the firewall into a L3 interface.

Thanks in advance.