If this setting is enabled, Windows Defender protects against Potentially Unwanted Applications. For more information, see https://blogs.technet.microsoft.com/mmpc/2015/11/25/shields-up-on-potentially-unwanted-applications-in-your-enterprise/.
If this setting is disabled or not configured, Potentially Unwanted Application protection is disabled.
Beginning with Windows 10 v1809 and Windows Server 2019, this functionality should instead be configured through the following Group Policy setting:
Computer Configuration\Administrative Templates\Windows Components\Windows Defender Antivirus, Configure detection for potentially unwanted applications.