Linked from
The 18 pages that link to Foreign exchange reserves, each with the reason it gives.
Capital controlsRelated: Controls can reduce reserve losses when demand for foreign currency surges.
Capital flightRelated: A central bank may spend reserves defending its currency as capital leaves.
Currency pegRelated: Reserves provide foreign currency for supporting a peg under pressure.
Hard currencyRelated: Reserve managers favor currencies that are liquid and trusted internationally.