Not every analysis needs to become software. A clear answer to a one-off question is often more valuable than a polished tool nobody needs twice.
The case changes when the same question returns with new inputs, different scenarios, or another person waiting for the result. Repetition creates a product-shaped problem: the method needs to be reliable, the assumptions visible, and the output easy to revisit.
An interface can preserve choices that disappear in a spreadsheet handover. It can show history, validate inputs, and let the user test a scenario without rebuilding the analysis.
The signal is not simply that the analysis is complicated. It is that the decision is recurring and the reasoning is worth making reusable.