I first knowingly came across it in a Steeleye Span song - The King - it was pointed out by my school music teacher:
The drones of a bagpipe or hurdy gurdy are (usually) open fifths. They create a space within which the melody moves.
This led onto a special liking for the use of parallel open-fifths - when two parts move in-parallel a fifth apart; as used in the early parts of the Tallis Fantasia by Vaughan Williams (parallel fifths are usually regarded as incompetent part writing in classical music - and often they are!):
But my favourite was to use a bare fifth as the cadence - the final chord - of some kind of unaccompanied harmony - as with the middle of the chorus from Malpas Wassail by The Watersons - the bit where the tenor slides up onto the high falsetto top note - which I found, and still find, electrifying.
Indeed the practice of sliding ('portamento') between notes, and chords, with all its dissonances-in-passing, is a marvellous aspect of some vocal folk music: