If the file is submitted as .zbd then there would be no confusion as far as scale of the parts is concerned. In the past we have had problems with the scale more than once, when we have processed the file in different units then what the student actually wanted.
You can see how it is going to actually get printed, by slicing the part layer by layer
You can look for grey areas in the part by yourself and fix them. Grey areas are due to non agreeing normals (and if all the normals are not pointing outwards) and they don't get printed.
You can have the part at the desired orientation, because there is a possibility of deformation in the part if they are not oriented in a correct way. Hence you can orient the part as you want.
You can calculate the price by yourself and if you want to pay less for the part you can remodel the part (by shelling, reducing the size etc.).
If we have .zbd's from students then it saves enormous amount of time and man power which eventually will benefit the students because we can get more projects done.