Both questions were answered in the article. The reason for precise directions is because otherwise people will complain, and if you ignore their complaints, they will complain to your boss. At the end you'll win, but you'll waste a bunch of time defending yourself.
The reason for not allowing cheating is repetitional. If you get a reputation for allowing cheaters, then all the cheaters will want to take your class, and eventually you'll have so many that your testing will be worthless. And if word gets out that your institution allows cheating, then your students will not be respected when they leave, causing harm to the non-cheaters and your chance at keeping your job as fewer people want to attend a school known for allowing cheats.