How often do reviewers receive notifications that they need to review transactions?

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• I am being notified that a transaction requires my action in the Needs Review tab. Why am I getting this notification?
• What happens when I mark a transaction as Permitted?
• Who can see the Needs Review tab?
• If a transaction was pending before Transactions Reviews was set up for my account, but has since settled after Transactions Reviews was set up, will that transaction require review?
• What can Spenders see?