ASP.NET 2.0 brought many enhancements aimed at reducing the amount of code developers have to write to perform typical development tasks. For example, most modern ASP.NET web sites provide user membership and role membership. We can see these features used in portals and forums. Forums, such as Community Server use membership and roles to authenticate users and then determine user permissions.
By default a new ASP.NET 2.0 application will create a SQL Express Database as the data store for the SQL Server Provider based features such as membership and roles. But using one database for the ASP.NET features and another database for the application code seems messy. The cleaner option is to store all data related to the application in one database. Now I realize a complex application may justify using multiple databases but trying to keep as much application specific data centralized in one database seems simple, clean, and logical.
To use one database for our new ASP.NET 2.0 site we create a database then use Aspnet_regsql.exe to create the necessary ASP.NET 2.0 provider tables in our database. The Aspnet_regsql.exe is found at drive:\WINDOWS\Microsoft.NET\Framework\versionNumber. The tool can be run without any parameters in wizard mode or from a command line with parameters.
See http://msdn2.microsoft.com/en-us/library/x28wfk74.aspx for more information.