WCF response object contents

I see WCF response types (i.e. the types of objects returned from WCF handlers) containing DTO types which in-turn contain the fields t开发者_如何学运维he client is interested in. Is this standard practise? Why not put the fields directly on the response type?

What WCF returns depends upon the binding details (TCP, HTTP etc) and the proxy. Transferring DTO is a standard practice.