Verbose Logging can be enabled to provide fine grain information within the RS Trace Log file. As a result of this logging level, the log file could become very large depending on the load of the Report Server. This information can be very useful when troubleshooting certain scenarios, however it is not recommended to leave the RS Trace Log settings to be in verbose mode. If verbose logging is enabled, you should disable it if no longer needed to troubleshoot your issue.
By default, the RS Trace Log file is not configured for verbose output.
The default location for ReportingServicesService.exe.config is C:\Program Files\Microsoft SQL Server\MSRS10.<Instance Name>\Reporting Services\ReportServer\bin for SQL Server 2008 and C:\Program Files\Microsoft SQL Server\MSRS10_50.<Instance Name>\Reporting Services\ReportServer\bin for SQL Server 2008 R2.
A setting of 4 for both the DefaultTraceSwitch value and the Components/all value, will place the logging level in verbose mode. For normal operation, these two values should be set back to a value of 3.