For Service policies that get applied to End User segments, by default separate policies are...

The default hostgroup type used can be changed from Configuration > General Settings.

Different hostgroup types can be used for monitoring End User segments for each Service.

While editing the Service one has the capability to select all sites or a subset of sites to include for monitoring.

When adding a Service Health by Location widget to a dashboard, one has the capability to include all locations or a subset (maximum of 10).

The default hostgroup type used for monitoring End User segments is ByLocation.