I use old-fashion serial cables for kernel development in 2014. It would be hard to debug without it. Sometimes you have bugs on physical systems that aren't reproducible in a VM and can only get any output via a physical serial cable.
For what it's worth, I also use serial-over-LAN to administer remote machines and virtual serial devices in VMs for security purposes.
For what it's worth, I also use serial-over-LAN to administer remote machines and virtual serial devices in VMs for security purposes.