Adding third-party tracking to your emails

Summary: how does the slider in email configuration works "Enable 3rd Party Tracking"

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We have provided some UTM parameters as a string in the field that appears after sliding the Enable 3rd Party Tracking slider in the email configuration. But it does not give the right results. In what cases should we use this functionality and how should we enter values in the fields that appears? Is it better to just use the External Tracking from the Email Defauls Configuration screen.