I had the same question - I posted my CV and was pleased to get a number of responses, including one from the CBS. They invited me to attend an 'informal interview' and sent me some material about the CBS. I thought that they had a real job or an interim manager position that they wanted filling, but was surprised and disappointed to find that all they were really offering was training in their proprietary toolset, and membership of their network/associaton. And the cost of joining the CBS is not small. So I asked myself - who gets the benefit?
Maybe the training does help new consultants win work. Maybe the network can provide benefits in terms of support from other independent consultants and the opportunity to share experiences and potential opportunities. But I would want to understand more clearly the value I would get from the training and other services provided, before parting with any cash.
Or maybe you and I are just unduly suspicious!