Typically if you are emulating a bigger conifer, like a pine, you may want to keep the bark - especially if it is flaky and aged looking- will it contribute to the image? If you are working in the dead wood style then you pick the bark off with a craft knife/scalpel/utility knife and gently scrub the bark with a brass brush to reveal the reddish inner bark. Can also be cleaned/lubricated with a little soapy water as you brush.
This technique may be done for several reasons- 1. it perhaps invokes the idea of a trunk sandblasted clean, or more likely, I believe, because 2. the orange-red color contrasts with the green and the white of any deadwood. 3. The smooth bark and color really highlights the movement of a snaking trunk whereas "flaky" bleaced grey or brown would tend to minimize the movement.
If the species in question does NOT have pretty under-bark then it is not worth the time, IMO, as the practice is purely asthetic...