The torch, radio or CO alarm that runs on AAs is only as reliable as the cells inside it. Ordinary alkaline batteries self-discharge, struggle in the cold and — worst of all — can leak and destroy the device while it sits in a drawer. Lithium AAs hold their charge for up to a decade, weigh less, and keep working in freezing conditions, which is exactly when you need them.
For anything you store and hope never to use, lithium cells are the sensible choice: buy them once, know they'll be ready years later, and avoid the classic emergency letdown of a dead torch full of corroded alkalines.