The dash, to performer one (a string player) is a bowing indication whose attack characteristics might range from relatively incisive to barely audible; to performer two (a wind player) it means a soft attack. Performer three reads this sign as tenuto: a term which is variously interpreted as “hold the note its full value” or “hold the note a bit longer than its full value.” Attack for this player has never been of great concern. To performer four, a dash means that the note is somehow invested with great expressive significance and, therefore, he is free to play in whatever manner seems most appropriate. And to performers five through infinity it means things the aural results of which are too horrible to contemplate.
Donald Martino, “Notation in General — Articulation in Particular,” Perspectives of New Music, 4/2 (1966), 47.