Publishing SQL Server information to Active Directory is only of any use if you have client applications that query Active Directory for such information.

When you publish SQL Server to AD, it publishes the SQL Instance and databases. One way that I could see this being useful is that you wouldn't need to configure your application connection settings. It can query LDAP://RootDSE to get your local domain information and then ask AD to give it a list of SQL Instances and databases.

I haven't yet seen an application that takes advantage of this feature. I would imagine that SQL Server creates an Application Partition within your Active Directory schema similar to DNS.

There is some further information here

http://www.sqlmag.com/Article/ArticleID/41841/41841.html

http://msdn.microsoft.com/en-us/library/aa174517(SQL.80).aspx