why not SQL Authentication?

From: Pavlos Kariotellis (pkario_at_eie.gr)
Date: 03/28/05 

Date: Mon, 28 Mar 2005 11:45:50 +0300

With Forms authentication and SQL Server, MS recommends creating a User
table and storing user names and password hashes to that table.
 http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnnetsec/html/SecNetHT03.aspThey go on proposing a Roles table and so on.I wonder why not just use SQL Server authentication and just try to loginwith the user supplied credentials?