Once you start implementing a real-world integration solution, you may have requirements that the built-in functionality in SSIS does not meet. For instance, you may have a legacy system that has a proprietary export file format, and you need to import that data into your warehouse. You have a robust SSIS infrastructure that you have put in place that allows you to efficiently develop and manage complex ETL solutions, but how do you meld that base infrastructure with the need for customization? That's where custom component development comes into play. Out-of-the-box, Microsoft provides a huge list of components for you in SSIS; however, you can augment those base components with your own more specialized tasks.
The benefit here is not only to businesses, but to software vendors too. You may decide to build components and sell them on the web, or maybe start a community-driven effort on a site such as
www.codeplex.com. Either way, the benefit you get is that your components will be built in exactly the same way that the ones that ship with SSIS are built; there is no secret sauce (besides expertise) that Microsoft adds to their components to make them behave any differently from your own. The opportunity is that you truly can "build a better mouse trap" — if you don't like the way that one of the built-in components behaves, then you can simply build your own one instead.
Building your first component may be a little challenging, but hopefully ...