From my experience, we keep the log levels as is.
Production usually has such high volume, that you would need a lot of disk space when you would higher the log levels.
And it has a negative impact on performance.
Only when a problem can't be reproduced on Test or UAT, you can consider setting higher log levels for certain components and/or logins.
The default log level is 0
The commands to use from server manager command line would be :
list evtloglvl for comp <comp_name>
To Change Event Logging Levels :
change evtloglvl %=<value> for comp <comp_name>
change evtloglvt %=4 for comp sccobjmgr_enu
This would change for all the events logging level to 4
To Revert Back
change evtloglvt %=0 for comp sccobjmgr_enu
Note that high level event logging will consume more space when they write to log files and the logs can quickly grow in their size.
Event log levels above 3 are recommended to be used when advised from Technical Support.
For further references please refer to :
Siebel Bookshelf : Siebel System Monitoring and Diagnostics Guide
Chapter : Configuring Siebel Server and Component Logging
Topic : About Configuring Siebel Server and Component Logging
Sub-Topic : About Events and Event Logging
Hope this helps.
Ramana Rao - Oracle