The only thing you need a calculator for is to perform computations, and that's where we draw the line.
There is nothing special about the fx-991ES calculator that any normal scientific calculator cannot perform, but the only thing that distinguishes it from other calculators is its natural display. This is the only reason that I use it as I can easily spot mistakes I might have made.
I recommend that you integrate/differentiate on your own, and then when you need to compute, just use the calculator. I also recommend that you don't use the integration shortcut available as it's very limited. Moreover, you will be taught how to integrate, so why use it when you can do it yourself?