Why wouldn’t you use SSL

ssl

A lot of web applications (Facebook and Twitter, for example) provide SSL support, but don't make browsing with SSL the default option–you have to opt-in manually. Is there some kind of major drawback to using SSL that I'm not aware of? It seems to me that browsing with SSL is clearly better than browsing without it. Why wouldn't these companies make SSL the default for their web apps?

Best Answer

It's all in the handshake.
A connection over TCP, like http://..., uses a three-part handshake:

Client --> syn,
Server --> syn ack,
Client --> ack

SSL uses a much longer sequence. This site says SSL (https://...) uses about 4 times more packets, and has 3.5x more latency than http://