First, if you enable the highest level of logging, you may get a performance hit. Generally, enabling the Debug level is only for troubleshooting. There are 8 levels of logging:
0 - Emergencies - system is unusable
1 - Alerts - Immediate action needed
2 - Critical - Critical conditions
3 - Errors - Error conditions
4 - Warnings - Warning conditions
5 - Notifications - Informational messages
6 - Informational - Normal but significant conditions
7 - Debugging - debug messages
Generally, if you want to be able to actually READ the logging files, setting to level 5 - Notifications would be enough. To capture the most information, set it to 6 - Informational.
#logging buffered info (if you want to see the logs on the PIX, "sho logg")
#logging trap info (or "notif" for less clutter)
I generally use the "informational" level on the trap (syslog) setting, and "notification" on the buffered logging.
#logging timestamp (add timestamps to logging)
You can enable the other logging options, but this could cause issues. (console logging will log to your console session, making it hard to see any commands entered or other information, Monitor logging will log to your remote access session (telnet, ssh))
Check out this URL about logging:
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a00805a2e04.shtml
