There are a couple of points that the users of the External Data Intelligence app must be aware off.
They are listed below in no particular order.
The segment when created is in a Draft status. The segment will evaluate when the campaign or program is activated and will follow the status of the campaign.
While adding a SOQL type criterion, the Compare <object> Fields List and Has Related Object Fields list will not be visible.
Within a single Filter Criteria, users cannot include both AND & OR conditions due to Salesforce restriction.
Users can define multiple criteria within one segment but all the criteria can be based on only one Object.
Users cannot delete configured Salesforce instances and Object configurations if there are Segments defined for those instances and objects.
Field Mappings cannot be deleted if the segments are part of any active campaigns.