I've been surfing around looking for clues about config.lua and also running experiments and I'm stumped.
What I assume LR is trying to provide is a way to have, for example, debug prints (log messages) in your plugin that, when shipped, is turned off but the end user can put something config.lua to enable the debug output go to a file and then that file sent to the plugin implementor. But, when I play with all the various options and APIs, I end up where if the plugin has foo.enable('logfile') the output will go to the log file and if it does not have it, the output goes nowhere. To rephrase, I've yet to discover how config.lua can enable or disable the logger's output.
This isn't horribly important but I'm hoping to write some general purpose routines and publish them in a git repo. I'm trying to make them useful to others beside myself.