Linked from
The 12 pages that link to Leavening agent, each with the reason it gives.
BakingRelated: Gas expansion creates the volume and porous crumb of many baked goods.
BatterRelated: Gas bubbles can make batter coatings lighter and more open.
PastryRelated: Pastry uses chemical, biological, and physical leavening to create lift.
CupcakeRelated: Leavening gives cupcake batter its light, risen structure.