A log file is created by the RUN command in your GAG_LOG: directory with the task name as file name and the extension .gildas; this log is printed by the SUBMIT command. If the user is still running the main program (GreG or Mapping, etc...) when a task completes, he (or she) is warned of the completion with the return status. Log files are not purged automatically, so that you should take care of that. They are intended essentially as a debugging aid if something goes wrong, but you can print them as archive of your data processing.
A command file is created in your GAG_LOG: directory to run or submit the programs. It is in principle deleted at task completion.