Javascript Server Sent Event

http://www.sitepoint.com/server-sent-events
Introduction to Server-Sent Events
https://www.airpair.com/javascript/node-js-tutorial

At which point does it make sense for us to use server-sent event? Is there any impact on the infrastructure in term of servers? Do we need to add more servers? Do we need to make any change to the firewall and load balancer?