CICS provides different levels of tracing to assist with problem determination. Standard trace level 1 is the default setting for each component to be traced within CICS.  The user can use CETR to specify what trace levels are set for each component of CICS. By default, INTTR, SYSTR and USERTR are set ON.  This means the master system and user trace flags default to be set on, and internal tracing is active. STNTR defaults to 1, as do all the STNTRxx values. This means standard trace component tracing defaults to level 1 for all CICS trace components (a consequence of this is that  by default a CICS system will incur the CPU usage to provide this level of internal CICS trace data).
There is a trade-off between the CPU cost in capturing trace data for problem determination, set against the ability to diagnose problems should they occur. Some customers elect to run with limited levels of tracing active on their system. While consciously choosing to use CICS trace does increase processing requirements, NOT using CICS tracing reduces the amount of problem determination information that is available for the CICS region. 
It should be noted that CICS always performs exception tracing when it detects an exception condition, so a minimum of first failure data capture is provided regardless of your CICS trace setting. However, exception tracing is by its nature limited in what diagnostic data it can provide, and it is very hard to perform initial problem determination without CICS tracing being active and all components capturing their trace data, to identify the flow of system activity and events in chronological order leading up to a failure. For this reason it is recommended that the default settings of all CICS domains and components should be used when tracing is active, to assist with problem determination. This is standard trace level 1 tracing. 

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