Traditionally we've published anonymous web sites on http (port 80). This is unencrypted, and the logic is we don't want to incur the overhead of encrypting and unencrypting what is essentially public information. This saves resources on both the server and the client browser. Authenticated or payment sites generally use https, which is encrypted and secure.
The reality today is that SSL encryption is no longer an expensive operation, and both the web servers and client browsers have more than enough horsepower to deal with it. Yes you can offload the SSL encryption off the web server to improve its performance, but I don't generally see the need for that.
There have been recent changes in the treatment of http web sites by Google. ...