why JSON return type is used instead ActionResult()?

For Example., Public Object M1() { return 25; } For above Method we can write Like this also., Public int M1() { return 25; } if return type as Object later we have to do DownCasting it will effect on Prformance.,if return type is int we can use value Directly .,like this is Scenario also Same

ActionResult is an abstract class .and then return values as drived class like more then one return class is there like jsonresult,javascriptrsult,contentresult,viewresult....etc

Performance is most concerns