Hey Suggy,
One thing I noticed is that the second docs link is for incident properties. These properties allows you to utilize Service Mapping to see affected services, and extrapolate affected business applications. These properties are very similar to that of Change properties that allow visibility very similarly into the Impacted Services and Business Applications.
As an example here is a screenshot the Operations workspace showing Impacted services and Impacted (business) applications:
I am not an incident expert, so I might be a little off in the details but from what I can tell it works pretty much the same as with change management:
The first property, Populate Impacted Services based on Affected CIs: Specifying a configuration item (or multiple using Affected CIs [task_ci] tab/list) can cause the related Impacted Services/CIs [task_cmdb_ci_service] list to populate utilizing (primarily) Service Associations [svc_ci_assoc] information. The second property, Populate the Business Application related list for incidents: will look for related business applications to those services and populate the Impacted Business Applications list [task_cmdb_ci_business_app]. The third property, Populate the Service Offering related list for incidents: is similar in that it populates another related list based on the Impacted Services/Business Applications. I have not set up service offerings so I am not entirely certain what tables or logic it uses.
I believe the first article is explaining that you should not specify a Business Application directly in the Configuration Item field or the Affected CIs related list (For the reasons the doc give and the other community memebers). Instead it provides the second article as a way to use the CSDM data to see how incidents of a infrastructure item impact business application and the services they provide/consume.
Hope this helps clean up the contradiction between the articles...
Josh
P.S. you asked how to populate the related list. Service Mapping is predominately how these lists get created. Service Mapping is the module/application from ServiceNow that provides associations from infrastructure to application services and ultimately business apps. Refer to the CSDM model image (https://docs.servicenow.com/bundle/vancouver-servicenow-platform/page/product/csdm-implementation/re...) and you can see how the individual infrastructure CIs are part of an application service (Manage Technical Services quadrant) which then is related to the business application (Design quadrant). You can read more about Application Service here:
https://docs.servicenow.com/bundle/vancouver-servicenow-platform/page/product/configuration-manageme...
