I'd imagine that the most common use cases will be the ones where people are already using excel, where the python is definitely an improvement over python, the default and only other programming language integrated with excel.

I used it to validate my an algorithm written in python, which was basically a many-step series of matrix multiplications

datanitro basically served as a debugger, letting me 'show my work' at each step in the algorithm, outputting matrices to excel spreadsheets as it ran. Excel provides a pretty good set for validating that the output at each step matched expectations, like conditional formatting where you can color cells based on their value and other math and graphing functionality

I can say for sure that I prefer using python with excel to using VBA, the only other previous option.