Spinning off a blog at Inside Higher Ed, the Dean Dad has a post on deciding what classes are essential:
My personal sense of it is that the distinction between core and periphery is largely a function of purpose. If your goal in life is to be an exhibited artist, then you might well decide that art is essential and history a frill. If your goal is to be an engineer, I could understand valuing a math class over a psych class. Since different students have different purposes, I wouldn't be surprised to discover that one student's frill is another student's priority.
But the questions go deeper…