I've never been much of a "joiner", but there is no denying the benefits I have found in being a member of the Professional Photographers of Canada. Here is an article that I wrote for Improve Photography, about some of the reasons for joining a professional photographer's association.
Improve Photography readers come from all over the world. Chances are there is a National Professional Photographer's Association of some sort in your neck of the woods, wherever that may be. If you are serious about your photography, you should consider joining it. Some benefits, like member discounts and access to resources, are immediately obvious.