For measurement technology, so-called "dummy loads", i.e. terminating resistors, are essential for transmitter calibration. They make it possible to operate the transmitter with power and to feed the radiated signal with perfect matching to an artificial antenna. The signal is not radiated but converted into heat - hence the often rather big heat sink and the limited operating time. This makes it possible to tune the transmitter without interference.
Attenuators are used to adapt the power - usually in the case of the transmitter - to a low power meter or assembly.