Students get immediate feedback since grading can be done regularly. This regular grading is made possible because all planning is done before the unit begins. Special Educators can easily follow the unit, modify assignments, and see what work has been done. Special Educators have access to all assignments and activities in the filing cabinet. Any subject can be incorporated into this model.
Parents can monitor student progress and see what has been done or what needs to be done.
That is the obvious fact that there is quite a lot of initial planning. However, this disadvantage is balanced by the fact that all of the planning is completed before I begin teaching each unit. I've found extreme satisfaction in not having to plan every night or weekend and instead dedicating that time to the assessment of my students' learning. Within the structure of this model, I always allow myself the flexibility to act on my instincts, even if this involves revising my initial plan. You can benefit from some of the planning I've already done by trying out the units I've developed for my own classes.