The purpose of the Default Sensor Policy is that it acts as a "catch all" policy if no other Sensor Policies are applied. A Sensor Policy is a policy that defines the detection and prevention settings for the Falcon sensor on a host. You can create and assign custom Sensor Policies to different hosts or groups in your environment.
However, if a host is not assigned to a specific Sensor Policy, it will inherit the settings from the Default Sensor Policy. The Default Sensor Policy is a "catch-all" policy that is enabled by default and has the
"Malware Protection" feature turned on. You can modify the settings of the Default Sensor Policy, but you cannot delete or disable it1.
References: 1: Falcon Administrator Learning Path | Infographic | CrowdStrike