Auditing is enabled when you register a SQL Server instance, and allows you to capture SQL events at the server level. For more information, see Register your SQL Servers. You can configure server audit settings during registration or later as your auditing needs change. For more information, see Server-level audit settings.
If you disable auditing for any reason, you can easily re-enable server-level auditing. On the Explore Activity tree, right-click the SQL Server instance on which you want to re-enable auditing, and then select Enable Auditing.