Using HTTP Request verb such as GET, POST, DELETE, PUT etc... enables you to build RESTful web applications. Read about it here: http://en.wikipedia.org/wiki/Representational_state_transfer
The easiest way to see benefits from this is to look at this example.
Every MVC framework has a Router/Dispatcher
that maps URL-s to actionControllers.
So URL like this: /blog/article/1
would invoke blogController::articleAction($id);
Now this Router is only aware of the URL or /blog/article/1/
But if that Router would be aware of whole HTTP Request object instead of just URL, he could have access HTTP Request verb (GET, POST, PUT, DELETE...), and many other useful stuff about current HTTP Request.
That would enable you to configure application so it can accept the same URL and map it to different actionControllers depending on the HTTP Request verb.
For example:
if you want to retrive article 1 you can do this:
GET /blog/article/1 HTTP/1.1
but if you want to delete article 1 you will do this:
DELETE /blog/article/1 HTTP/1.1
Notice that both HTTP Requests have the same URI, /blog/article/1, the only difference is the HTTP Request verb. And based on that verb your router can call different actionController. This enables you to build neat URL-s.
Read this two articles, they might help you:
Symfony 2 - HTTP Fundamentals
Symfony 2 - Routing
These articles are about Symfony 2 framework, but they can help you to figure out how does HTTP Requests and Responses work.
Hope this helps!