Charcoal is often used as a component in orchid potting mix because it is inert (will not decay), allows flow of air through the potting mix, and some believe, it binds certain toxins from the metabolism (breakdown) of the organic components of the potting mix. Charcoal is made in Canada from hardwood (mostly sugar maple) through a pyrolysis process
Most commonly, charcoal is only one ingredient. Most potting mixes have both organic and inorganic components. These are needed in the proper balance to help keep moisture ot the roots, provide some nutrition, permit air movement through the mix, and help to firmly anchor the plant in its pot. We include charcoal in all of our custom mixes.
In our experience, we have found that adding charcoal helps "sweeten" the mix. It prolongs the life of the media so you don't have to re-pot as often. Also, as the media breaks down, which happens naturally over time, the charcoal will minimize any foul odour which rotting fir bark can cause.