Peat just isn't used by our members, it's just different... and needs to be repotted often, and watered less. I heard it is great for the oncidium alliance.
Anyways charcoal is supposed to act as a sweetener for the mix and it suits all orchids. It has absorptive qualities and can pull out and neutralize toxins, etc. It is very useful but I don't add too much of it, because the production of it is not healthy for habitat conservation. ... It also doesn't decompose like bark so it does keep the mix open, sort of like what perlite and sponge rock would do