I loved my old HP calculators (HP-67 and 28S) and it's fun to have a new one. I have not used calculators much in the last 20 years except to do quick calculations, scale things, check vector magnitudes, etc. Like you, if I need to do anything heavy duty, I use use Python, Mathematica, or recently Matlab. I've also played around with Sage recently which has promise but is a bit clunky.
What brought on this purchase was that I had to replace my simple HP solar calculator (that I used for quick calculations) because its display was going out. I got an HP 35s and was disappointed in its limitations (fixed 4-level stack, a buggy ROM that has not been updated since its introduction more than 6 years ago, etc.) So I looked at getting a 50g but heard there was a new one coming out. So I limped along with my Android Droid48 app and my HP 35s (mostly the former) until I could get this new calculator.
So what will I do with it? Grossly under-use it most likely! But I also hope to learn how to use it in more detail. I'll probably write some programs to simplify certain calculations that I have to do from time to time such as compute quaternions for certain typical rotations. But I'm sure that mostly I'll do those same simple calculations that I was doing with a much simpler calculator!