Linked from
The 10 pages that link to Steric effects, each with the reason it gives.
ChemoselectivityRelated: Crowding can obstruct access to one functional group more than another.
Alkyl groupRelated: Bulky alkyl groups can obstruct access to reactive sites.
Coordination geometryRelated: Crowding between ligands can favor geometries with more space.
GeminalRelated: Two groups on one atom can create distinctive local crowding.