When going to bed/sleep - I personally don't want to deal with a scheduler and setting times, and looking at what time it is now, and setting a task to finish in 40 minutes etc - I'll do all that just once saying "this is what I want to play when I am going to sleep" etc.
When it is set up and just as I fall into bed, 20 seconds before my head hits the pillow I just press the "I'm going to sleep now" button, and the program takes over from that.. This is "Fire and Forget" for "Counting Sheep"
A sleep feature does seem like it would make for a nice extension of the scheduler. You could configure its settings once, then activate it using a single button afterward, where it would fade the audio out over time before shutting down, or just sitting there in silence. Likewise, there could be the option to fade a theme in over the course of a few minutes at a specific time, for use as a 'gentle wake' alarm clock.