RestrictAnonymous has implications on the operating system side. It should not have any impact on SQL Server. Basically it determines if someone can make a null connection and if they can, can they enumerate security accounts. This is all on the OS side.
The optimal setting is 2, however, that setting should not be configured without rigorous testing as you may find apps breaking.
How to use the RestrictAnonymous registry value in Windows 2000
K. Brian Kelley
@kbriankelley