From the Apple Support site:
The Broadband Tuner allows you to take full advantage of very high speed Internet connections that have a high latency (5 Mbps or greater). The installer tweaks some system parameters.
The installer increases the default values for the size of the TCP send and receive buffers. With larger buffers more data can be in transit at once. A startup configuration file is also updated so that these changes will persist across restarts.
That’s interesting; I’ll have to play around with it at home.