You have a RESTful API. Good. You now want to communicate with it. You need to write some code (an SDK) to do the requests, or you can generate it automatically

You have a RESTful API. Good. You now want to communicate with it. You need to write some code (an SDK) to do the requests, or you can generate it automatically. If you write it yourself, you have to do it for every language you use, since you can't reuse SDK between different languages. Even worse, if you can't generate an SDK every person who access your service will end up writing different code to talk to your RESTful API. There are other advantages, like automatic documentation, easier management of versioning, schema/type verification, ...