One merge carries one branch back. The Merge Board is for when five branches each found something. Tick the branches you want, set aside the ones you only half believe, and choose what you need at the end: a Summary of what they found, a Decision with pros, cons and a recommendation, or a Draft ready to hand over.
Each branch shows a short summary, and sessions save themselves, so you can come back on Thursday to the board you left on Tuesday. The Merge Board is on the Pro and Team plans and during a trial.