This is one of my favorite features. Wasn't able to figure out how to set up my somewhat complicated guest + iot wifi vlan setup through the web interface, but it was pretty straightforward through the config files. And now I have it backed up in case I ever need to set it up again from scratch.
If you straddle the worlds of preferring a "normal" router to a custom built box but also want to keep your configuration history in git I think OpenWRT may be the best option.