I have tried it a few times. It's good if you're new to the game. Otherwise not so much. I found I leveled slower by using it, as it's suggesting to take the longest possible route usually. Basically following roads everytime, when you could take an easy shortcut. Especially if the shortcut involves a bit of fall damage, it's out of question. The "go here" spots don't also update if you take a shortcut, and then the waypoint arrow points to wrong direction. But perhaps it has been updated since then.
In the wake of clawing, gouging, or cutting out their own eyes, the demon hunter undergoes a change and begins to see the world anew. Rather than perceiving the world as a normal individual would, they begin to understand the world as a level of energy, viewing everything around them with a fel-touched sense of sight that, “can see to the end of the universe,” as was stated by Illidan Stormrage himself to Vandel. This sight has no issue in distinguishing inorganic matter, organic matter, and even the type of magic being utilized or welling within a particular individual. A fledgling demon hunter without the proper guidance might stumble around for months or longer trying to figure out how to see in the wake of their loss of eyes, while those who were trained under the guiding hand of the Illidari might have been given an easier time coping with this newfound sixth sense due to being around so many of their comrades and those who had also walked the path before them.
2. Your DH needs supplies on a regular basis. They can only carry so much food, clean drink, medical potions and whatever else they want/need at a time. It's pretty realistic that they would need to visit a market every so often, and large faction markets will have the most variety and types of items to choose from. (My DH has been a recluse in the wild for some time, and she is stinky, dirty and has eaten some questionable stuff. This isn't really ideal and a Dalaran doughnut would be pretty flippin nice.)