Is it some sort of pre-built GUI scaffolding?
Why would I Want it instead of a WinForms UI, which is quick to set up?
What does it give me that I would have to spend
Visual Studio Shell enables developers to rapidly create and distribute their own custom tools by building on a streamlined Visual Studio IDE.
A Visual Studio isolated shell-based application has full access to Visual Studio services and supports customization and branding. There are several ways you can customize a shell-based application, as follows:
The Visual Studio Shell is freely available as part of the Visual Studio SDK. Visual Studio Shell is royalty-free for building and deploying applications.
Your isolated shell application can be installed on any computer that has the Visual Studio 2008 Shell (isolated mode) Redistributable Package.
Each isolated Shell-based application to be deployed must have a valid shell load key (SLK). The SLK is uniquely related to the application and cannot be used to load any other application. You can obtain SLKs on the Visual Studio Extensibility Developer Center Web site.
After you obtain a shell load key (SLK), you must add it to your Shell project. Follow this procedure to add an SLK to a project that was created by using the Visual Studio Shell Isolated template.
Note: Everything said up to this point has been copied and pasted from various Microsoft documentation pages. A good place to start might be Walkthrough: A Basic Isolated Shell Application.