Using SSIS configuration file (.dtsConfig) to manage environment variables, such as server connections and source file paths, can contribute greatly to portability and manageability of an ETL application that comprised of SSIS packages.
We utilize configuration files extensively in our DWBI implementations to alleviate the complexity of promoting builds (DEV, TEST, PROD), server migration and deployment to multiple ETL servers. SSIS solutions can be readily deployed to different environments with simple changes to these XML-based configuration files without having to modify a single package.
For instance, one of our DWBI implementations employs 2 separate servers to "load balance" the processing of flat files (web logs) made available on a central file server. The same SSIS solution is deployed on these 2 ETL/staging servers (SQL Server, SQL Server Agent, Integration Services). But the solution instances are driven by slightly different configuration file specifications. Below is the over-simplified data flow.
The configuration file on each server specified the same source file server, destination DW server, and other control variables with the exception of one flag to indicate whether to process odd- or even- hour source files and another to indicate which one of the 2 target ETL servers to stage the extracted data.