The biggest benefit is the lack of the cord. Most of these units hook around your ear and can sit there waiting to answer a call. The one I have has a button you can hit when you get a call (it makes a ringing sound in your ear). The Blackberry needs to be in the area of you to work, whether it is on your belt, sitting in your breifcase, on your seat or in the Holster. It works very well, and is something I would not give up now.
Oh and it puts you in the group of us that look like we are schizophrenic and walk around and talk to ourselfs.