It allows you to reuse your Excel or PowerPoint Web Applications in other web pages – such as this blog.
When the original file gets updated, the other location is updated too. So, I could publish my SharePoint 2010 Overview presentation in SkyDrive, and embed it in a Blog entry called SharePoint Overview.
If the messaging ever changes, or I want to alter it…. all I have to do is update the source and the blog entry is kept up to date.