While much has been written about the inherent benefits of delaying Social Security benefits to age 70, a fundamental challenge in the real world is that the decision cannot be viewed in the abstract. The decision to delay Social Security isn't just about the value of delaying, but also about the money that must be spent from the portfolio to sustain spending in the meantime, and/or the decision to allocate money towards delaying Social Security and not towards other fixed income investments or a commercially available lifetime immediate annuity.
Yet a deeper look reveals that when viewed from an investment perspective, the decision to delay Social Security actually represents an astonishingly valuable "investment" return, based on the internal rate of return of the cash flows that it provides over time. While it is certainly unlike other more "traditional" investments, in that its return is based not on interest rates or market performance but on the longevity of one's life, for those who do live a long time the decision to delay Social Security can produce real (inflation-adjusted) returns of 4%, 5%, or even 6% for those who live into their 90s and beyond.
Calculated in this manner, the reality is that for those whose greatest retirement "risk" is living far past life expectancy, the decision to delay Social Security can actually be a highly beneficial investment, with a real return that dominates TIPS, is radically superior to commercially available annuities, and even generates a real return comparable to equities but without any market risk! Of course, there is still an aspect of "mortality risk" inherent in the decision to delay, but for those who are most concerned about living a long time and funding a long retirement, the decision to delay Social Security - even if it means partially spending down the portfolio in the meantime - can actually be the best means to securing a successful retirement, by converting the uncertainty of market returns into the certainty of higher Social Security payments!