"Longevity risk (outliving one's savings) is a risk that many rational retirees who rely on savings withdrawals are less likely to shoulder, so they'll tend to spend less so as to preserve those assets. The alternative is to transfer some, if not most, of the longevity risk to a third party ... [A]nnuities, when used to bridge that expense gap, mitigate the risk of the unknown lifespan. This then leads to a retiree who is more comfortable spending down savings on expenditures that exceed basic needs."