Why should your desk be far from the door?
Feng Shui makes a big deal about the location of your desk. You should never have your back to the door, though that is often the case. Why shouldn't you have your back to the door? Because we don't like being startled or being taken by surprise especially when sitting down and that's just what can happen when you have your back to the door.
Your subconscious mind addresses this potential threat by being on alert. It's subtle but it does take energy and focus from you. Test it out by moving yourself so that you are facing the door rather than having your back to the door and see how you feel. If you can't do this in your office, try it in a restaurant. First sit in a seat with your back to the door, then shift so that you are facing the door. Which feels better?
Safety is a foundational principle of Feng Shui. One can not feel in harmony with one's environment if fear, even low grade fear, is in the mix.