That's for maximizing the power transfer, which is important in radio applications because you want to maximize SNR (and because this is the condition where no

That's for maximizing the power transfer, which is important in radio applications because you want to maximize SNR (and because this is the condition where no power is reflected). Power applications (like speakers or the power grid) are generally concerned with maximizing efficiency, which you get by lowering source impedance as much as possible.