For those of you that have not played with the SSA calculators, you might want to, especially if you are over 40. Fill out the year by year worksheet to see how much each year of employment has contributed to the "pot" that is the basis for your PIA.
Social Security is progressive, it replaces a higher percentage of income for low earners than for high earners. There are two "bend points" that are important to note. After a certain point, you are working for very little in additional annuity, although you continue to pay the tax at the same rate. At that point, your taxes are largely subsidizing other recipients.
I have a lot of zeros in the later years, as I retired early a number of years ago. That has not had a huge effect for two reasons. One is the bend points, but the other is the indexing under the National Average Wage Index. It's not what you earn over your lifetime, it's the indexed amount of what you earn. For the positions I held in the early years of my career, that indexing has been a huge factor. The indexed amount of income from those positions is actually much more than what they pay today. Yay, general wage inflation! I wonder if the NAWI calculations will covertly reduce the annuities for younger folks, because they did not live through the inflation of the late 70's and 80's, when wages kept up with inflation. Filling out the worksheet year by year and multiplying your taxable earnings for Social Security by the NAWI factor will tell you if you are benefiting from wage inflation and by how much.
There's a lot of discussion of SWR's considering the impact of Social Security over at early-retirement.org. One idea is you can use a higher withdrawal rate and draw down more assets in the early years of retirement because the Social Security annuity replaces the need for some of these assets later on. That might work if you are a few years out from collecting, but I would not make that bet if I were much younger than that.
I'm going to be collecting the annuity in the not too distant future. It is not enough to live on in HCOL Silicon Valley, but if I waited until FRA, it would be more than what the MMM family spends in a year, even after Federal income tax on 85 percent. YMMV.