When making a movie it is important for all of the various departments to have all of the right tools to get the job done. To make this happen you need to have a detailed line by line budget divided by department. This is for all sized films, whether you have a 5 thousand dollar budget for a short film, or ten million dollars for a feature.
If your hair department needs chi flat irons, a hair iron, and hair shears, then you have to know how much money you can give the department to buy these (if you know early enough, buying products online usually saves you money) and how it effects how much money is left for other departments. If one department goes over budget, than you have to find the money somewhere, from another department. (and trust me, you’ll want to get that chi flat iron for the hair department)
