Custom REST Resource Endpoints

In the previous part-1 of this series we talked about the Rest API and how can we define the Rest API Plugin type in your system. In the previous example we have defined the REST Plugin in your custom module, add some get()/Post() methods for reading and writing operations. 

Now in this series of Rest API or Rest API part-2, we will discuss more about REST API and we will show how to define REST API using a custom controller class.
Now the question arises here why do we need this custom Rest API controller class over the REST API plugins?