I don't think a BC is needed when free diving. You will want to add a little bit of weight though using a weight belt. Just don't over weight yourself, obviously. With that said, some places require certain types of flotation devices to be worn in certain body's of water, like rivers for example. In those cases, having a vest that can act as a flotation device for you, but still allows you to be able to dive underwater, may be necessary.
