When you deploy your app to the web, you need to consider how your users will first experience it. If they've the required version of Silverlight installed, your app will load and run normally. Otherwise, you'll need to convince them to install or upgrade.
When you implement and test your app, you probably use one of the default web pages in the Silverlight project templates for Visual Studio. These pages contain boilerplate HTML that provides a full-page display, some error reporting script, and a bare-bones install experience. This makes the pages good for testing, but unsuitable for deployment.
For deployment, especially to general public, you should provide an experience that effectively entices users to install or upgrade Silverlight in order to view your content.
This QuickStart describes some user interface (UI) recommendations, summarizes some of the implementation details, and provides links to more complete documentation.