GET requests a representation of the specified resource. GET should not be used for operations with an effect like an action or change in web applications. GET may be used arbitrarily by robots or crawlers and could have consequences if used for sensitive information or an operation with an effect.
GET appends the returning variables and their values to the URL string but POST does not. URLs are limited in length, at least, should be to some extent. When using GET in AJAX requests, its important to keep in mind that some browsers (IE) will cache the results of a GET request. So if you, for example, poll using the same GET request you will always get back the same results, even if the data you are querying is being updated server-side. This issue could be fixed by creating a unique URL unique for each request by appending a timestamp or key number of requests. Overall, GET is used to retrieve remote data.
POST submits data to be processed, a common example is information from a form. The data is included in the body of the request. The POST can lead to the creation of a new resource, the updates of existing resources, or both. Since the request will change something, sometimes see your browser ask you (or warn you!) about resubmitting form data if you hit "back".
A POST has information in the body of the request while a GET passes information in the URL. POST will keep the URL cleaner and can send much more information easily. Some types of information can only be sent via a POST, like a file upload or a form. Thus, a POST is used to insert/update remote data.
