The main reason is to share your contact information with other people. You have the ability to hide individual contact components if you wish. You also have the ability to change things like your address or phone number whenever needed.
You can add a picture of yourself, and even add your device if you wish. There is also a section that allows you to add some information about your person and a link to some additional information.
You are required to have a login to fill out an officer report, award recommendation, or change of officer form as well as a few other areas of the web site. This brings the benefit of not needing to fill out that basic information every time you submit something such as on the old web site.
