A best practice is to remove the branches after they are merged.
When you remove a branch, you remove an association between a branch and an application. Removed branches and their rulesets are not available when you create or copy records in the application.
Note: Removing a branch does not delete its contents from the system. To delete a branch from the system, see Deleting a branch from the system.
To remove a branch, select Actions > Remove from Application for the branch you want to remove.