What is the advantage of locating an antenna tuner near the antenna feed point, over locating it near the transceiver?

An antenna tuner (or transmatch) matches the impedance of the antenna system to the 50-ohm output of the transmitter. When an antenna is mismatched, a high Standing Wave Ratio (SWR) exists on the line between the mismatch and the tuner. If the tuner is located near the transceiver, the transmission line running out to the antenna still operates with a high SWR. A high SWR on a coaxial cable causes increased power loss as heat. By placing the tuner right at the antenna feed point, the mismatch is corrected immediately. This allows the entire length of the transmission line back to the radio to operate at a low 1:1 SWR, drastically reducing transmission line losses and ensuring more of the transmitter's power is actually radiated.