DataContract, DataMember, Message based

It appears they are using DataContract, DataMember to serialize the data for the WCF service. It is still necessary if the hosting layer is removed and going directly to the Service Layer? Does it matter if they stay serializeable? Is there overhead doing this? Should I remove it and if so how do I go about this? I took out the hosting layer and made the necessary changes and it works, I just wanted to know if all the serialization is necessary or has any impact.

Thanks
Dennis