Impedances are deliberately miss-matches more often than matched. Impedance match is useful to couple the most signal and the least distortion due to reflections. Impedance match is important to high speed cables like video, data and network cables, cable TV and antennas. High speed electronics use series termination where the source matches the trace impedance but the destination does not, producing a single deliberate reflection and minimizing the power used. Audio cables are very short relative to audio wavelengths so most audio circuits are voltage based, ie the source is much lower impedance than the load. For loudspeakers this provides a form of feedback called buffering. An exception is some microphones where electrical noise is an issue. Analog telephone lines are used with a complex impedance that varies with frequency because the cable impedance is actually somewhat lower than classic telephone circuits. The termination network has a 100 Ohm impedance that matches the cable at high frequencies but rises to about 1K at low frequencies where even the phone line is less than a quarter wave length. Electrical busses are very useful, including AC power distribution, but in order to control the amount of power used by each device, each has an impedance that draws only as much power as that device requires. Computer signal busses have largely been abandoned due to the problems with reflections that result from multi-point connections.

I should also mention that many impedance matching issues exist with mechanical and optical systems. A gearbox is a impedance matching device and lenses and mirrors are an optical impedance miss-match.

An r.f. transmitter to its feedline and antenna, yes.

Amplifier to 'speaker, possibly.

A solid state (audio) amplifier is a voltage source. The load is not matched to the source's impedance. The lowest value of load impedance is related to the power supply's ability to deliver current. Nothing to do with impedance.

A valve (vacuum tube) amplifier does need load matching - which is done with a transformer.

For example, if a source with a low impedance is connected to a load with a high impedance the power that can pass through the connection is limited by the higher impedance. This maximum-voltage connection is a common configuration called impedance bridging or voltage bridging, and is widely used in signal processing. In such applications, delivering a high voltage (to minimize signal degradation during transmission or to consume less power by reducing currents) is often more important than maximum power transfer.

Amplifier and speakers

Transmitter and antenna