SMFPRMxx parameters confusion

[deucalion0]

Hello all, I hope you are well.
For the past week I have been researching everyday, trying to make sense out of something that should be straightforward but just does not add up for me.
The parameters I am confused about are the SYS and SUBSYS parameters, both are documented here https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.4.0/com.ibm.zos.v2r4.ieae200/smfparm.htm
For SYS:

SYS(options)
Specifies the SMF recording options and exits for the entire system. The options are as follows; if the same option is specified more than once, the system uses the first valid operator reply.

For SUBSYS:

SUBSYS(name,options)
Specifies the SMF recording options and exits for particular subsystems.

I thought that having this would apply to the whole system:

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SYS(EXITS(IEFACTRT,IEFUJI,IEFU83,IEFU84,IEFU85,IEFUTL,IEFU29,IEFUJV))

Therefore this would not be required:

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SUBSYS(STC,EXITS(IEFACTRT,IEFUJI,IEFU29,IEFU83,IEFU84,IEFU85))  

But I know that the STC part of the SUBSYS parameter is important, and it seems that that above,

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SUBSYS(STC,EXITS

is doing something more than

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SYS(EXITS

but I just cannot figure out the difference here.
To summarise my question, when I read the IBM documentation here https://www.ibm.com/support/knowledgecenter/SSDTFJ_7.1.0.2/com.ibm.itcamfad.doc_7101/was_agent_install_guide_z/was_agent_shared/chapter_adv_dc/insd0051119541.html , why is SUBSYS required when SYS is at the system level, isn't the SUBSYS definition included under the SYS definition?

Any help or advice here would be much appreciated, as after a week of research I still cannot find an explanation as to the difference.

Thanks!

[vasanthz]

What differences are you seeing between SYS and SUBSYS, since you say "it is doing something more than"
I have been struggled with SMFPRM recently and found that if you specified SYS paramater (the entire system), you do not need to specify it for the SUBSYS (subsystems).