The UDF will allow you to define a multi-valued parameter in reporting services (there are lots of other uses as well), and pass that parameter into a stored procedure.
Within the stored procedure you would use it like this:
(@strMy_User_ID_List is the passed parameter)
select *
from tblUsers
where numUser_ID in
(
select *
from dbo.dbo.fnSYS_Split_Comma_Separated_List_Of_Integers_To_Integer_Table(@strMy_User_ID_List)
)
