Why do that when you could just connect it to the LAN and put it on a separate VLAN?
Because the built-in networking stack on printers is garbage and having to install drivers on every client sucks.
I’ve never had issues with networking or drivers with my Brother printer. I don’t have any Apple devices, but on Windows and Linux I just use the drivers that come with the OS.
I’ve not had a Brother printer so, can’t say from experience. My Epson Ecotank needed a driver to work. Setting it up on an RPi 3B with a CUPS server took care of it.
Because it’s a lot simpler and avoids the issue of dealing with printer drivers on all your machines.
I could see the argument that it’s more air gapped this way. Without having physical access to the Pi (or at least SSH access), it’d be hard to get any network connection through USB.
But personally, I just blocked outgoing traffic from the printer.
