A serial console allows you to see the boot logs even before the Linux kernel has started booting! Therefore, a serial console attached to your Raspberry Pi can help you find causes of problems like the following:A new Linux distribution that you flashed on your Raspberry Pi does not boot.Your Raspberry Pi boots into an older kernel even though you installed a newer kernel provided by your distribution maintainer via apt/pacman/dnf.You installed a new kernel using apt/pacman/dnf but now the Ethernet port does not work and you can't SSH...