The ArcWeb Services implementation of REST provides a simple alternative to the SOAP protocol. Since there is no intermediate SOAP layer, there is no need to work with a SOAP toolkit to interact with REST. Instead, make direct calls to the API through a Web browser by creating a URL that contains all the desired mapping criteria and a map is returned.
REST and SOAP contain different functionality. For example, SOAP can calculate the best map around the geometry while REST can rotate the orientation of the map.
Only SOAP can use custom maps created using the ArcWeb Site.
See the link in the Related Information section below for more information.