Why would you use a reed relay over a semiconductor switch or electromechanical relay when switching RF relays?

Reed relays are very linear over a large span of frequencies, typically ranging from DC up to 20 GHz.  Semiconductors need filters and suffer from inter modular distortion.  This means additional components need to be used.  The reed relay by itself will do the job and are ideal when switching low signal level RF loads.  The reed relay’s size is much smaller than the electromechanical relay and comparable in size to the semis.