I feel like in an undergraduate degree program, that is where students are trying to develop basic skills and find exactly what they want to do with the field of graphic design. Grad school sounds like it is more geared for students who know what they want to do with their careers and are trying to further those skills. I think grad school is also a place of experimentation and, though you know what you want to do, you may even find another corner of graphic design that you love.