Cast of no discernment is essential for those in theatre (8,7)

I believe the answer is:

informed consent

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'essential for those in theatre' is the definition.
I know nothing about this answer so I can't tell whether this works.

'cast of no discernment' is the wordplay.
'cast' indicates an anagram (letters are dispersed or cast around).
'of'+'no'+'discernment'='ofnodiscernment'
'ofnodiscernment' is an anagram of 'INFORMED CONSENT'.

'is' acts as a link.

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