Excel is a powerful tool. I was solving system of differential equations with Newton method in it. Sometimes it is easier than in Matlab (or Mathematica) if all you have is good understanding of how step-wise equations should look like, but not the differential equations themselves. Those steps may include if statements, for example.
Had to do a similar project and it took me three full days of back and forth with another software before I found out EXCEL rounds small numbers in very weird ways.
Also, in EXCEL functions/formulas and data/values are wildly mixed.
(Not mentioning a plethora of other mildly infuriating quirks here)
Kind of serious, the lack of smooth scrolling makes Calc really horrible to use on a touchpad or with large/differing sized cells (formatted sheets with headers and such)
Call me crazy, but the admittance matrix hw (Gaussian, G-S, Newton, N-R, etc.) I did last semester was much more intuitive for me on MATLAB than on Excel... but I'm gonna get screwed for that because a vast majority of companies would never bother to pay for MATLAB (+ Toolboxes) licenses.
There is always Octave.
And I am not claiming that Excel is better than Matlab. There are lots of tasks where Matlab is better, or where it is not even possible to use Excel with any efficiency. And yet, Excel IS a powerful tool for scientists and engineers. Not just for accountants.
We have a single licence for matlab installed on an old laptop in the lab. I find it easier to program in Excel than try to reserve the laptop and go to the office (sometimes you reserve it and after arriving you find out that the last guy never returned it so you spend extra time trying to find where it is or who has it)