title: Passing an interface instead of an object instance
body: <p>Take for instance the SqlBulkCopy.WriteToServer() method.  One of the overloads takes an IDataReader as the parameter.  My question is, what's the benefit/advantage to passing an interface to a method instead of the object instance itself?</p>
  
  <p><a href="http://msdn.microsoft.com/en-us/library/434atets.aspx" rel="nofollow">http://msdn.microsoft.com/en-us/library/434atets.aspx</a></p>