Why would you use a single fixed pulley to lift a box if the mechanical advantage of the pulley is 1?
Well, I am not sure if it is what you want...basically, the person can take advantage of his weight to help in lifting the load.
The pulley and rope together can be used to "change direction" of forces. In this case to lift, say, a box of books with your arms can be a little bit difficult. Using a rope and a pulley you can hang from one end using your weight to do the job for you! so basically your Weight (force