The only subject area outside of parliamentary government where I have heard of the use of shadow committees is crisis management. You don't want your crisis management team to burn out before the crisis is resolved. It can make sense to have a fresh bench of talent that has been in the information loop while remaining ever ready to supply energy and perspectives.
The other area where a shadow committee can be helpful is where the subject is so important that the potential infusion of new ideas may make the difference between success and failure.
Remember: The insiders have the power to act but they lack the time and perspective of the outsiders. The outsiders have the time for ideas but they lack the power to act.
After a failure, the list of opportunities or dangers missed by the insiders can be quickly assembled by the outsiders. The insiders may shout, "Why didn't you tell us?" and yet - unless there is a formal shadow committee system - we know the answer: The insiders were too busy doing what they were doing to listen to any suggestions from the outside. The outsiders knew their ideas would not be welcome.
Got a major project? Consider a shadow committee.