The pros are that you can implement additional 
functionality and access data from DLLs from within SQL 
Server. If you need to do something that can be done only 
in C or C++, or if you have data that can be accessed only 
outside of SQL Server, you can still provide a link to it. 
The biggest con to extended stored procedures is that they 
run in the same process space as SQL Server. So an errant 
DLL could overwrite memory and cause SQL Server to crash or 
even corrupt data. The biggest safeguard against these 
problems is thorough testing of the procedure