Dashboards are extremely important tools mostly used for monitoring systems and environments. The main idea of these tools is to keep clients up-to-date with arriving or changing data on the server side. For that, the most popular technique used in web applications is based on ajax polling. With ajax, the client polls the server for data every time the content of the page requires an update.

Once the idea of monitoring is to show actual data information, there are several problems with current ajax technique. The first one is scalability. The number of requests made to the server can be extremely high if the frequency of polling is set to a small value. Not only the server but also the network can become saturated with all those requests. On the other hand, if we set a high value for the pooling frequency, some information may be lost or delayed. Another problem is that the response may not contain any data. So, in these cases, ajax polling overloads the server for nothing.

http://fernandorubbo.blogspot.com.br/2013/06/using-websockets-to-implement-dashboards.html