Do you mean the problem gave him a formula and asked him to describe the graph? There's no educational value in using a calculator to generate that graph compared to the graph just being printed alongside the formula. You don't learn by being given the answers before you try to do it yourself. Instead, you need to come up with an answer yourself then check if it's right. The calculator could be useful for checking, but only if the student doesn't use it while they're doing it themselves, otherwise it's no better than copying answers out of the answer book.
The value I can imagine with generating graphs on a calculator would be trying a large number of graphs that are too numerous to print in the text book or to organize in some big table of graphs. That's also the value of a scientific calculator which is faster than looking up trig functions in tables, or a basic calculator that's faster than doing arithmetic by hand.