When writing a story in the second person, writers refer to the main character as "you," as if the writer is the voice of the character's conscience. "You need to get out of here John (the character). Your career is at risk and now you may also lose your wife." Second person narrative can give readers an insight of the character's motives at some parts of the essay, but it can also be confusing for readers. The audience may question if it is the main character or another person speaking or even if the writer is talking to them.
At some points of the essay you may want to provide a generalization and for this purpose use second person. For example: "When you don't know if your business venture is legal in a certain state, you should ask the authorities or a law office." However, this technique can have certain drawbacks, as it is not clear whether you refer to a specific audience (students, readers of a magazine) or the general population. To avoid such confusions, you can use the pronoun "one" instead of "you."
Essays you write may be targeted to specific people, such as university professors, supervisors at work or politicians. The second person refers to them and it cannot be a matter of confusion, but its use is inappropriate for another reason. As in your face-to-face interactions with these people, you need to show respect and acknowledge their ability to understand what you want to say. Second person is too patronizing and they may take it as arrogance on your behalf.
Essays are not marketing material and you must not use second person to make the reader feel engaged and involved. Whether it is a school project or part of a publication, the reader has chosen to go through your essay and does not need tricks to stay focused. Especially on occasions when you want to sound authoritative, such as explaining the attributes of steel or the hardships of soldiers in Iraq, second person can lighten the atmosphere and compromise the essay's formal style.