Why it matters?
Radio signals grow weaker as the distance between the transmitter and receiver increases; the maximum distance for Wi-Fi depends on the standard, with 802.11a allowing 95 feet and 802.11n topping out at 230 feet.
The data rate for a given client will adjust dynamically depending on the distance and Signal strength. As the distance between AP and client increase, the Signal will decrease. As the signal decrease, the data rate cannot be maintained. The transmitting device will drop its data rate to the next rate in order to maintain the connection.
802.11b access points operate at the following data rates - 1, 2, 5,5 and 11Mbps. As the link quality deteriorates, the access point will automatically throttle down to lower data rates in an attempt to maintain a connection. In some cases you may not want the AP to throttle down to lower data rates in order to support higher bandwidth applications. Most AP’s allow you to configure the data rates based on the 802.11 standard.
Most modern Wi-Fi analyzer provides insight into the Signal and data rates being achieved at various locations within your environment.