I rebuilt one of my nodes recently due to a software glitch unrelated to Bitcoin Core, so I thought I would save some time by using tar to backup the blockchain onto an external drive before purging the drive in the machine.  Something about the backup was corrupted in the process, and caused me to dick around with my core settings for an hour before I suspected that the blockchain directory may have been at fault.  Sure enough, I purged the blockchain files, reset my systemd service file and my config file to their original state, and bam it's working.  After all that, I realized I wasted the time that it took to backup the blockchain, the time it took to restore the blockchain, and the hour of dicking around with my settings.  So, yeah, it was all for nothing.