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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