Debugging Linux startup issues with JournalCtl

My computers running Linux are very reliable but every so often a spanner will be thrown in the works and the computer will refuse to come up beyond a command prompt. When this happens you have to look at the logs to try to work out what is happening in the system and how to get it going again.
This happened to me a couple of days ago when I turned on the computer and instead of resuming after hibernation, it threw up a number of error messages and then asked for the root password for maintenance (or there was the option to press Ctrl-D to continue). The Ctrl-D option simply put the computer into a loop where it ran a FSCK only of the boot drive, and then failed to resolve any issues, and came back to the same message. Or the option was there to enter the password which took it to a terminal to see what could be done.
Since the advent of systemd, its companion journalctl (with the -xb parameter) is what is recommended to look through to try to determine what the problem is. This took quite a while and it wasn’t particularly obvious what was actually happening. The main issue I noticed immediately was no networking; the wired network adapter in the computer appeared not to be functioning, indicating that part of the startup of getting the adapter up and running had not happened. I tried a whole lot of things but eventually concluded I would have to try a live CD to see if this was a hardware issue or if it was something with a driver. 
The network turned out to be a red herring once it was realised that there was no home path in the file tree (i.e. /home was completely missing) and fairly soon running fsck over /dev/md1 revealed some errors. Once these had been fixed, rebooting the system brought up KDE normally and suddenly everything was working again like usual.
It isn’t the first time this has occurred and I think last time we just threw in the towel and reinstalled. At the time of trying to resolve this issue I was downloading netinst and live images to burn to a pen drive and try to reinstall, but finding this relatively simple solution sorted the issue without having to take that complex, lengthy and very inconvenient route of putting everything back together. And what seems an obvious issue may actually not be the problem at all. The network adapter not working turned out to be a non issue as soon as the disk issue was taken care of and a reboot initiated.