Socket buffers decouple the sender and receiver, so that the sender does not need to block while waiting for the receiver to receive all bytes. Client buffers improve the efficiency of the client when performing several small write operations. 

By default, the client buffer size is zero and the socket buffer size is determined by the underlying operating system. If you specify a non-zero client write buffer, remember to call zTcpClient_Flush to ensure that buffered bytes are written to the underlying zSocket.