Suppose 1 million users request at a time to the server. What will happen - server will create 1 million thread for every request. But its impossible - server will be completely unresponsive. So we will make a better approach. Suppose 1 server can have such resources that it runs smoothly with 20 threads. Now we will implement a thread poll which will queue all of the request and process 20 requests from the queue.
Suppose 1 million users request at a time to the server. What will happen - server will create 1 million thread for every request. But its impossible - server will be completely unresponsive. So we will make a better approach. Suppose 1 server can have such resources that it runs smoothly with 20 threads. Now we will implement a thread poll which will queue all of the request and process 20 requests from the queue.