If you want to remove an email message from your Inbox of your Gmail account, then Archiving is used. But If you delete a message, it directly goes into the Trash, and that will be deleted certainly within the 30 days. If you archive an email message, it will not be deleted, rather it will just remove a message from your Inbox. Archived messages can be used again in the future if required. So it is recommended to archive messages instead of deleting them from your Inbox.