??? To me it seems legit - the phones need their own network environment to work properly, so why not put them into a VRF and let them have what they need there, without risking interference with the rest of the configuration. And then you need a way to manage them without having to put the management device to the same VRF, which is when the controlled leak comes into play.
Until it came out that it was 3CX, I was expecting it to be some extension of telecom’s xDSL, where it is quite common that the address space in the telephony VLAN is unrelated to, and potentially overlapping with, the address space in the internet VLAN and in the customer’s home network.
Of course you could use mangle rules to assign the routing marks rather than VRF, but since it was working in ROS 6, I can understand well why @nichky has taken the easier path (easier back then, that is).