Generate before you buy
A render can be reviewed before it is attached to a product. This lets the user verify the moment and viewpoint first instead of discovering a data-entry mistake after production.
One moment can support several layouts
Different products have different aspect ratios, bleed requirements, and safe areas. Those production changes can move labels or recompose decorative elements without changing the underlying sky state.
Provenance should survive fulfillment
The production file should remain linked to the render identity used at checkout. That makes it possible to distinguish a printing issue from a calculation issue and to regenerate the same chart later.