What is Soft State for OData Service?
Soft state mode allows SAP Gateway runtime to process various requests in a single session of ABAP application server, same as the stateful behaviour. There is only one difference in the behaviour of the application server that is after the session times out the server creates a new session and processes the request as usual instead of breaking the request processing with a time-out exception.
For users, the change of the application server sessions remains transparent and therefore there is no data is lost in the client session.
Use of Soft State
We must use soft state mode for those applications which are built on legacy functionality in the backend, primarily in the case where the functionality includes initial loading/caching of big amounts of data for a single request for example price calculation.
With the help of the Soft State, we can reuse those resources/functionality for the subsequent requests of the service which has been loaded during the initial load. Therefore the most important advantage of using soft state is its considerable performance optimization of an OData service.