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 into it to uninstall that kernel.
- Your Raspberry Pi does not boot at all.
- You are learning kernel development and want to see why the change that you made is preventing the kernel from booting.
- You have so many Raspberry Pis that you have run out of displays to connect to and just want to watch the boot logs to sanity check if they are booting correctly or not.
I actually already have one of these USB serial adaptors that I’d been using to flash Tasmota software onto my Sonoff WiFi power switches.