During the week I have been working with SQL Server 2005 Standard Edition and 2005 Express Edition for a website. I have specifically been looking at using SQL Server 2005 for Authentication as opposed to using the standard authentication that comes with ASP.NET when you configure an ASP.NET application in Visual Studio 2005. When you enable authentication for your website an SQL Server Express database (MDF file) is automatically created and the connection string in your web.config file is also changed to point to that SQL Server Express database.

Why is the standard authentication model not appropriate for all uses?

A couple of reasons I can think of:

1. If you wanted your development environment and your application environment to work together seamlessly then you might want to consider using SQL Server Authentication, or at least get both environments to use connection strings that are similiar or the same.
2. If you wanted to change or add to the fields provided by the regular membership model provided in ASP.NET and in particular have those fields stored in a proper database table.
3. If you wanted to use a Database Management System other than SQL Server. Perhaps you want to use MySQL or MS Access. You can also use Active Directory and XML as an authentication model.