On the fly and per Analysis an end-user with Advanced Tab permissions can update variables, logging levels, etc. within the report in an ad-hoc fashion. The benefit here is that if one is just running quick tests or looking to identify issues, one need not make changes permanent in the RPD, etc. just to run a few quick tests.
In order to modify any user variable or session variable such as loglevel, disable_cache_hit, locale, etc. (must be marked available for updating) a user can just specify the override in the Prefix Section of the Advanced tab.
The syntax would look something like, SET VARIABLE [VariableName] = value. For example: SET VARIABLE LOGLEVEL=4;
The loglevel override example would set the users session logging level to 4 so when the query runs the next time a log for that query will appear in the nqquery.log file.
When hierarchical columns are use, they restrict access to may components of an Analysis, however, the Prefix section is still unaffected in the Advanced tab so this functionality is still possible even when Hierarchical columns are used.
Check out these BI Publisher tips including functions & calculations so you can understand more about the production and support of BI Publisher reports.
Ultimately the goal of commentary in OBIEE is to have a system for persisting feedback, creating a call to action, and recognizing the prolific users.