No idea - which airports are these? The DRDF we used to use was really useful for radar (lost aircraft, aircraft below radar cover, providing a rough QDM, or even simply as a freecall was being received to direct your eyes to the right part of the radar display). Also for tower, assuming the aerial was somewhere on the central part of the airport, meaning you could often find a stuck mic (or anonymous tranmission!) aeroplane on the airport. Unfortunately it was deemed surplus to requirements, with all the other fancy kit we had, and seemed to disappear from many uk airports.
Interesting if someone's seeing the benefit again!