The --debug flag on the server start command does at least two things:
Additional logging during the startup of the server that shows the settings in use
per-request logging that continues after the server is online and logs a line to the console for every request that is processed by Runwar
The first bullet can be very handy for debugging your server starts in Docker, and the lack of this information has recently caused a lot of confusion for people-- especially in regards to what cf engine they are using. However the second bullet point is not desirable on a production system as it adds a lot of stuff to the console out and the server.out.txt log file. The --verbose flag will show the start up information but not activate the debug logging inside of runwar.
There is additional start up debugging in runwar that would be nice to have --verbose control, but this flag for now should at least help until we can refactor Runwar further.