The biggest, most important benefit of having a shadow jury in place, according to the text, is that, because the shadow jurors would actually hear the same testimony as the actual jury, they can provide:

Question

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Shadow jurors provide critical feedback on the trial's proceedings, allowing attorneys to adjust their strategies accordingly. They do not have access to the actual jury's deliberations or personal relationships with the defendant.

The Biggest, Most Important Benefit of Having a Shadow Jury