Linked from
The 15 pages that link to Associativity, each with the reason it gives.
GroupRelated: Associativity is the group axiom that makes products of several elements unambiguous.
Vector additionRelated: Regrouping three or more vectors does not change their total.
Abelian groupRelated: Associativity is a group axiom independent of commutativity.
CategoryRelated: Associativity ensures that a chain of morphisms has an unambiguous composite.
Inverse elementRelated: Associativity helps establish familiar laws for two-sided inverses.