So, your app needs to generate some content, such as images, on the fly and display them. You don't want to write a completely seperate program web program to take some parameters in the request and generate the image, and you don't want to have to deal with writing a temporary file to disk, then deal with the issues of cleaning up those temp files later. So, what to do?
With Iowa, you can let your application be responsible for the content that it needs to generate, and Iowa will give it the urls that will access this content.
The images below were not served from static image files. Rather, their data sits inside a simple database and was queried out of that database and delivered using this inline content capability. A more interesting use of this capability would be the generation of graphs or charts from live data that may vary by user/session/page.