Mark gave you some very good information concerning the difference between the two types of timber surfaces. The hewn surface is definitely alot more challenging to work with, and it will separate the men from the boys.
Having taught traditional timberframing courses using hewn material that as a group we prepared as part of the course, I have seen good tradesmen walk away from the layout work on the rough surfaces, saying that it took too much concentration.
To me I enjoy working with the hewn timbers, and in nearly every case the students would tell me that each time they now look at an old barn, home, or outbuilding that was created in years gone by, how they appreciate the work that must have went into its construction.
and Brad I also am really interested in your comment about not recommending hewing, especially when you took the time to attend a course and learn the skill. Could you broaden out your comment alittle I am sure for those that are viewing this thread.