That's a great question. During live courses we have limited time with you and must condense content to the most important topics that require hands-on experience, plus consider terrain and weather issues. Books are often limited by publishers to a degree many people would be surprised by. This can leave important content behind. Digital content is not restricted by any of these things and, therefore, can thoroughly cover topics and be as long as the author needs since you can study the material at your own pace. This greatly augments book and live learning.