They reduce the negative ion's that are created by our electronic devices that are often in our bedroom with us at night. These devices too are contact points for the energies that are on the other side.
I know that my daughter has one in her room and she is really happy with it. I have a candle holder salt rock in my room. She also has a dream catcher on her bed frame.
Now looking to when I put it in the room was about the same time I put a Dream Catcher over the closet door. Its in the same room, and my husband has noted that I am sleeping a lot deeper than I was. I have noted I am not up in the night to use the washroom like I was. So there could be something to the combination of the two.
I would thin that anything that will absorb negative energy can go to do no harm in trying. They are not expensive, and the pink one's have the nicest low light glow so you can sleep with one on and not be bothered by it.
If the crow has chosen you as your spirit or totem animal, it supports you in developing the power of sight, transformation, and connection with life’s magic.