We got a whole bunch of TIs a few years ago. I never knew why. I still don't know why. They cost a bunch of money, I know that. The district seemed to feel we needed them.
I mostly use them to demonstrate how to use them.
I have used them (today, in fact) to save time demonstrating patterns. But I only do that maybe once a year because patterns can be found easily enough. This pattern today was a bit more complicated. Our periods are short. And the kids needed the calculator practice for the upcoming NECAPs (New England Common Assessment Program).
I have always had a sneaky suspicion that TI has a huge PR thing going on to convince us that we need these things.
The comments of this post are interesting. When I took calculus I had a graphing calculator but found it a hindrance to learning what happens in a graph. I spent my time monkeying with the calculator instead of analyzing what was happening in the graph. I certainly couldn't use the calculator results in an exam because I was never as sure of the results as I was when I did it manually.
I am very interested in student, parent and instructor feelings about graphing calculators.