Erroneous people sometimes get in your database. The Delete Person flow step can get rid of them.
Use the flow step in a smart campaign.
When you delete a person, all of their historical RCE data will be deleted as well. It cannot be undone.
When you drag in the flow step it will automatically be set to delete from your CRM as well.
You can delete from Marketo and not from your CRM, like so:
Removing the person from your CRM only works with Salesforce. If you delete a person from Marketo and choose to keep them in Salesforce, they will be recreated in Marketo if their Salesforce record ever gets updated.