Extended Log : It creates an extended log,including 
warnings and other messages.Need to disable this option for 
large load testing scenario otherwise the system will 
become very slow.
Extended log options : 
1)Parameter Substitution
2)Data Returned by server
3)Advanced Trace

Standard Log :It creates a standard log of fnctions and 
messages sent during script execution to use for debugging.
Disable this option for large testing scenarios.