Communities of Practice are very powerful forces and are well documented in their benefits to an organisation. There is however a potential rat hole that you can go down by allowing anyone to start a community based on what they think the business requires.
This commonly happens when the company provides technology such as SharePoint and allows anyone to establish a ‘community’ space at a whim.
A much better practice is to have a defined process for establishing a community of practice which includes such thing as a community charter and management validation step. The community leader (or person who wants to start a community) presents their case for such a community to management and seeks their endorsement. Only after such validation should the community be brought into existence. It also prevents or at the very least challenges the creation of very small communities which have been proven to be much less effective than large CoPs.