PXE, or network boot. It is basically never used (and rarely enabled, if ever, by default) by the individual, but can be helpful in, for example, a large scale OS deployment. Say IT has to get their corporate image version of Windows 10/11 installed on 30 new laptops. They could write a ton of flash drives, but it'd be easier to just host a PXE boot server and every laptop just listen to them.
V6 specifically in that instance would just be for the reason of "we need to move away from v4 anyways"