Imagine you have a smart campaign flow that uses Send Alert to remind a sales rep to call a hot prospect. It sends one message every day until the rep makes the call. You could use Remove from Flow in a trigger smart campaign once the prospect has been contacted to stop further alerts. It's like a smart campaign ejector seat for a person.
This would normally affect people that are sitting in a campaign flow's wait step.
You can remove people from a campaign's flow by using the Remove from Flow flow step.
Find and select the smart campaign you want to remove people from.
This functionality is meant to be used within the flow steps of a smart campaign.