Linked from
The 9 pages that link to Four-wheel drive, each with the reason it gives.
RallyingRelated: Many top-level rally cars use it to improve traction on changing surfaces.
Off-road vehicleRelated: Driving all four wheels can improve traction on loose or uneven ground.
All-terrain vehicleRelated: Some ATVs use it to improve traction on loose or uneven surfaces.
Off-road racingRelated: It improves traction on loose surfaces and steep, uneven terrain.