System Statistics...do I need them? - (DBMS_STATS.GATHER_SYSTEM_STATS)

Any one have advise, references/links/docs, and procedures for using, colleting, and maintaining System Statistics (DBMS_STATS.GATHER_SYSTEM_STATS).

I have never used them but am looking to se if I can *help* further improve the performance of database application code. I will not re-write (the application) bad sql but as a DBA I do feel obligated to maintain and improve the database or create the best playing filed possible (for the bad sql ;o) ).

By not having System Statistics am I not giving the database code a better chance?

Thanks

PS
I believe (know) nothing is free in life nor with Oracle...there are no "silver bullets". Having any stats is an attempt and will change sql plans...for better *OR* for worse. I assume this rule applies to having System Statistics, no? Simply...what is the chance things run worse with System Statistics?

PPS I found these;

Doc ID: 	Note:149560.1
Subject: 	Collect and Display System Statistics (CPU and IO) for CBO usage

Doc ID: 	Note:153761.1
Subject: 	Scaling the System to Improve CBO optimizer

Chris Marquez
Oracle DBA

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