In practice
The platform splits what you lost into budget and rank. Budget-lost share is a spending decision; rank-lost share is a relevance or bid problem, and they need different fixes.
On a small, high-intent keyword set, chasing 100% is usually the right call. On a broad one it is a way to overspend.
Why it matters
It answers the question ROAS cannot: how much demand is still on the table.
Related terms