Comment by PeterWhittaker

Summary: If you know learn a little, you realize that each packet might be separately acknowledged before the next one is sent. In particular, note this quote: Net::HTTP doesn’t set TCP_NODELAY on the TCP socket it opens, so it waits for acknowledgement of the first packet before sending the second.

By setting TCP_NODELAY, they removed a series of 40ms delays, vastly improving performance of their web app.