When you sleep and are trying to program your mind your micropone or reciever is turned off or at best badly muffled. However, on some level it is reaching your brain. The problem here is state dependent learning. Meaning if you are in a state of mind your memory will be greatest of that event while occupying the same mental state which is unconscious.

I do believe there is benefit in doing this. Secondly, I do think the best way to program your mind is to relax completely, listen to music that supports your goal, visualize goal & using an affirmation in present tense.

I think the benefit in listening to them while you sleep is that on some level you will be familiat even if that level is unconscious. Second there is always a chance that you could dream about the material, find insight, & remember it when you wake up. That potential is a huge plus don't you think?

If your interested I could suggest excellent books on this written by a licensed psychologist.