Custom styles allow users to customize the appearance of Windows Sidebar so that it fits the style of other UI elements, such as the Aero Glass colorization or an actual third party theme. Designers could save their visual styles for Sidebar so that other Windows users could apply them. Designers would not necessarily create these files on Windows Vista - Sidebar Styler is backward-compatible with legacy operating systems as well.
Gadgets - these mini applications which are managed by Windows Sidebar can now take full advantage of Windows Presentation Foundation - a powerful managed code-oriented framework for presenting rich visual compositions such as vector graphics, 3D drawing, animations and more. In addition to that, it could be used in conjunction with the Communication Foundation in order for the Gadgets to connect to services and provide frequently updated information. Using compiled class libraries also helps protect the intellectual property of developers because the actual source code is not distributed.
The tight integration with the core of Windows Sidebar allows the application to extend the current set of features of Windows Sidebar by allowing users to customize its appearance and by providing a more powerful framework for building Gadgets and visualizing information.