I know from my hobby of ancient coins that a lot of discoveries have been made in the recent past—i.e. since the fall of communism— through the use of metal detectors.
Yup, a lot of Byzantine-era caches were found, apparently buried by those fleeing the barbarians (such as the ancestors of the Bulgarians). There was also a massive uptick in ancient coin forgeries, right down to the phony concretions covering the supposed finds. Metal detectors should not be shunned by archaeologists, particularly since they wind up not learning of the existence of sites they should know about in order to study them.