Export clause in Pipe protocol

Good evening, I have this kind of bird.conf: https://pastebin.com/6pMkJFix I understand that in the Pipe protocol I need the 'import' clause to import in master table routes learn by BGP. But I don't understand why in the Pipe protocol in combination with BGP is useful to have the 'export' clause and why having an 'export' clause in the Pipe protocol based on communities, I mean I will filter routes based on communities on BGP 'import/export' clauses, not in the Pipe protocol. Thanks, Fabiano