disturbed: what the OP is referring to is the ability (seen in previous versions of iTunes) to "join" tracks together so that they always play together (aren't broken up into individual songs) and there is absolutely NO gap between the tracks, nor any "cross fade." This is only important if you are listening to, for example, a live album, where you don't want a gap in the applause nor the jarring effect of applause being cross-faded. There are some other occasions where it is handy (audiobooks might be another example), but it's not widely used outside of those particularly examples.