Sliding Windows Continued
Large window sizes can cause problems on a network with lots of traffic or on one that does small data transfers.
If the sending host waits too long, it will retransmit the data. Then, that sending host may receive an acknowledgement of both the original and the retransmitted data.
In general, networks that transfer small amounts of data should use small window sizes, however, if the receiving computer is forced to acknowledge every data packet due to a small TCP sliding window, network traffic increases disproportionately.
TCP window sizes can change during the life of the connection, so the window can actually be expanded or contracted as needed to make the communications more efficient.