Linked from
The 11 pages that link to Marginal analysis, each with the reason it gives.
BottleneckRelated: It helps judge whether expanding bottleneck capacity is worth its cost.
Sunk costRelated: Only costs and benefits that change with the next action belong in the decision.
ElasticityRelated: Point elasticity applies responsiveness to changes near a particular value.
MicroeconomicsRelated: Many microeconomic predictions turn on whether one more unit is worthwhile.