Spreadsheets are excellent at one thing: applying a fixed formula to a fixed input layout. They are categorically bad at three things: documenting which assumptions were active when the number was produced, surviving structural change to the problem, and exposing where a result is sensitive to a quietly-flipped input. A spreadsheet answer is therefore a calculation, not a derivation — and the gap between the two is exactly where most quantitative work goes wrong over time.
A synthesised result fills the gap by recording everything the spreadsheet hides. The premises are typed and explicit. The inference steps are named and ordered. The domain of validity is attached to the output, so that a reviewer can see immediately whether a downstream change has invalidated the result. When an assumption changes, the engine re-derives only the affected portions of the graph rather than recomputing the entire artefact, and the audit trail shows exactly which downstream nodes were touched.
The practical workflow is to keep the spreadsheet for what it does well — capturing concrete inputs and surfacing the final number — and route every derivation through Quantm before committing to the result. The engine produces the synthesised answer plus the chain of inference; the spreadsheet records the inputs and surfaces the output to the reader. Used together this way, the two artefacts produce a quantitative deliverable that holds up under audit, which is the whole reason the work was done.