Recommended IPS signature set

i understand from several emails in this list is that UTM or IPS
devices enable only subset of signatures for detection as well as
blocking - it is being termed as 'sane IPS', 'out-of-box IPS' ,
recommended etc..

is there any criteria (standard or non-standard) used in categorizing
signature as 'recommended'?  is it based on CVE priority?

Thanks
Ravi

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