Server-Sent Events utilize a regular HTTP octet streams, and therefore are limited to the browser’s connection pool limit of ~6 concurrent HTTP connections per server. But they provide a standard way of pushing data from the server to the clients over HTTP, which load balancers and proxies understand out-of-the-box. The biggest advantage being that, exactly as WebSockets, they utilize only one TCP connection. The biggest disadvantage is that Server-Sent Events don’t provide a mechanism to detect dropped clients until a message is sent.
Possibly an alternative to using websockets for server-client communication (when the communication does not need to be two ways).