HOTSPOT
You are designing a SQL Server Integration Services (SSIS) package configuration strategy.
The package configuration must meet the following requirements:
Include multiple properties in a configuration.
Support several packages with different configuration settings.
You need to select the appropriate configuration. Which configuration type should you use?
To answer, select the appropriate option from the drop-down list in the dialog box.
Answer: 
Based on “https://msdn.microsoft.com/en-us/library/cc671628.aspx” both configurations – “XML” and “SQL server” are good for the mentioned case. Maybe “SQL server” is more flexible. But the question “You need to select the appropriate configuration. Which configuration type should you use?” is not enough.
http://bi-polar23.blogspot.com/2008/12/choosing-ssis-configuration-location.html
I agree. This article basically said sql server and xml are the same regarding features and its just a matter of who is running the package and what they’re accustomed to. You’d figure the person writing the program would be unbiased toward the capability of both options
https://www.mssqltips.com/sqlservertip/1434/using-xml-package-configurations-with-integration-services-ssis/
After further googling:
A single XML configuration file can store as many configuration settings as you need, allowing you to use the same configuration file for multiple SSIS packages. However, every property that is specified in the XML configuration file must exist in the SSIS package else an error is raised when opened in BIDS (or Visual Studio).
It’s not exactly the execution, but maybe that’s a problem?
https://www.mssqltips.com/sqlservertip/1405/sql-server-integration-services-ssis-package-configuration/
This shows the sql server configuration created for one package in one project and doesn’t addess reusability by other packages. I guess its possible. It’s really all a mystery.