Refer to RFC 2414 on how initial congestion window size is calculated.
This is the maximum value a TCP cwnd can grow to. Note that even if an application uses setsockopt(3SOCKET) to change the window size to a value higher than tcp_cwnd_max, the actual window used can never grow beyond tcp_cwnd_max. Thus, tcp_max_buf should be greater than tcp_cwnd_max in general.
Do not change the value.
If the initial cwnd size causes network congestion under special circumstances, decrease the value.