IMO, never.

Rule #1: Perfection is attainable

Rule #2: The universe is not constant: Screen sizes change, browsers, screen types, technology, new competitors come up changing people's expectations, people's tastes change, you expand into new demographics/demos/sales channels which react differently than existing demographics/sales channels, etc.

Ideally this work is done with a marketing/programming/operations team all in one, so all aspects are considered, with their trade offs, to forward on a collective understanding of solving user pain points.