I think one important thing to note is that you would typically set up a template package with all of your variables and package configs all set up. By copying and pasting this package you are able to quickly build up your ETL.

However, when using this method in conjuction with the SourceID attribute as mentioned you will need to explicitly generate a new SourceID for each package you copy and paste based on the template. Otherwise, all packages will have the same SourceIDs.