Prioritization is a spatial problem. High impact, low effort — do it first. Low impact, high effort — skip it. The 2×2 makes that argument visually obvious in a way a ranked list never does.
Purpose: force the prioritization decision into a physical gesture. Dragging something to the bottom-right corner is a more honest act than ranking it #8 on a list.
Impact →
Quick wins
Big bets
Fill-ins
Skip
Effort →