The school of thought that plays non-music elements just to fill space is wrong. Period. As someone who programs in a PPM market, this has been proven again and again, over and over. You NEVER stop the music/not play music when you don't have to. There is no reason to condition the listener in order for them to notice less when actual spot loads increase and the entire stopset is filled with spot. The majority of listeners are out after the first spot regardless of the length of the break. And wouldn't it make sense to have music playing when they check back in 2, 3, or 4 minutes? Of course it would! Because if they check back and you are playing non-music elements that you don't have to, you lose them for another 2, 3, or 4 minutes.