XML serializes only public members of the class. You use SOAP or Binary serialization when you need to transport data across the network. SOAP sends it using HTTP Protocol which makes it most interoperable while Binary serialization is known for its light and compact nature. Web Services uses the SOAP Serialization and Remoting uses the Binary Serialization. Infact Serialization is always neccessary when you need the object to transfer across a network. Advantage of using the SOAP or Binary serialization is that you can serialize the entire object and all those object that are being refrenced by it. This is why it is also called Deep Serialization.
