JSF ActionListener, ValueChangeListerner and Ajax

ActionListener and ValueChangeListener can update UI and do some side effects rather than the ActionController which process biz logic and carry out page navigation. However in this way the whole page is refreshed. Ajax is better in that it refreshes only part of the page's DOM tree, thus makes it much faster. So usually you would not notice the delay it takes to send request and get back a small piece of html from server.