What do I benefit from
ssl_session_cache set in nginx.conf when I using https? See here.
When using SSL-Session-Cache, the performance of keep-alive connections over SSL might be enormously increased.
When the server does have it enabled, it is not necessary for the client to do a full SSL-handshake every request, thus saving time and cpu-resources.
You can read up more here: http://vincent.bernat.im/en/blog/2011-ssl-session-reuse-rfc5077.html
And here is a benchmark: http://www.peterbe.com/plog/ssl_session_cache-ab
Hope this helps.