qb.conf is the main configuration file for Qube as a whole for the local machine; you can specify supervisor, client, and worker settings in there. If the local machine does not have a worker or supervisor installed on it, those settings are ignored.
The qbwrk.conf file is a centralized worker configuration file that resides only on the supervisor. The supervisor reads this file and loads the settings in it into memory as "remote configurations" for the workers.
When the worker starts up, it reads its local qb.conf file first and builds its local config. Then it asks the supervisor if it has a remote config for it. Any settings in the remote config trump settings in the local config.
In this way, you can leave almost all the settings in the workers' qb.conf at the default (there are a few settings involved in getting the worker to the point where it can ask the supervisor for a remote config, "bootstrap" settings). You would put into the qbwrk.conf any worker settings that you would like to manage from a centralized place (on the supervisor). Then, if you want to change a setting for 1 or more (or all) workers, you can simply make the change on the supervisor in qbwrk.conf.
When you run "qbadmin worker --reconfig", the supervisor re-reads the qbwrk.conf, rebuilds the worker configurations in it's memory, and sends an instruction to the workers to re-request their remote configs. The workers contact supervisor and request their remote configuration, receive the new settings and apply them immediately.
