The other great thing was the built in motivation, that you could get your homework done faster with only a little effort. I remember one of my earliest successes was a classical mechanics solver where you could put in whatever you knew (time and distance) and it would spit out whatever it could come up with (average velocity and average acceleration assuming initial velocity of 0). Pretty handy!

And of course you can have this device in your hands during many classes making it so at a moment of enforced boredom you have the opportunity to learn.