One of the least appreciated steps in the drywall process is the process of anchoring drywall to the desired surface. It is not as easy as just taking the drywall and anchoring it to the wall with screws or nails. There is a lot of work that goes into measuring the drywall to ensure that it fits on the wall that it is going to cover. Ensuring proper coverage is done by taking multiple measurments of the surface being "drywalled." In those measurements the "hanger" needs to account for multiple different scenarios: cutting the drywall to match angles and curves, measuring out any areas where a hole will need to be cut into the drywall, knowing how to anchor it to different types of surfaces, and shimming out areas to ensure that the drywall is level when anchored.
Along with being very detail oriented during the cutting process the drywall "hanger" also needs to pay attention to the way the drywall is being hung to make the job for the drywall finisher a little easier. To be able to do that the person hanging the drywall needs to be able to: off set seams in the drywall to avoid railroading (multiple seams in a row), knowing where natural light will affect seams or angles (natural light makes a seam/angle more noticeable after project completion), and ensure that there are no large gaps between the drywall. All of those variables, along with the process of hanging, contribute to the best possible outcome for any drywall project.