Although bracketing doesn't work well with active subjects, as Nicole mentioned, I tend to look at the practice as being insurance. Not just insurance that I have the exposure nailed, but insurance against other factors that might damage the film. Other than with local subjects that can be conveniently re-shot, film is probably the least expensive element in making the image.
So, with LF B&W, I'll often make a backup shot at the same exposure, and then bracket plus and minus by a stop. For color, the bracketing is 1/3 stop. The trick is to keep the film organized so the backup sheets are not processed at the same time as the primary film.
Similarly, when shooting color on important projects, I'll separate the film into smaller batches, and have it processed on different days. That way, if the lab has a problem, the whole project isn't lost.