To prevent transmitting signals over the air when making tests✓Bonne réponse
To prevent over-modulation of a transmitter
To improve the efficiency of an antenna
To improve the signal-to-noise ratio of a receiver
Explication
A dummy load substitutes a non-radiating resistive load for the antenna, so the transmitter can be tuned and tested at full power without putting a signal on the air and interfering with other stations. It does nothing for antenna efficiency or receiver noise.