Reality checks serves 2 purposes.

1: It is something that assures you that you must be dreaming, in order to have your conscious mind truly aware of your reality that your in a dream.

How do you know you are dreaming without a way to check?  A reality check is something that assures you that you are dreaming. Most easily done using your own body, but some use other things.

And, they serve to prevent you from jumping off a cliff, thinking you can fly because you thought you were dreaming but you were wrong. You need to be sure you are dreaming, before getting all crazy with the tricks your going to be pulling.

Also, it is easy to forget you are dreaming, and become distracted, doing RC helps you remember its a dream, as its on going.

I don't recommend anything that could distract your sleep, such as head phones, as I think it makes your sleep lighter or distorted, and may contribute to foggy dreams. I recommend deeper sleeps for vividness.