the answer is it depends on individual situations .
Of course.
But in most situations, your investment time horizon isn't the X years to ER, it's the total years you have left.
^This.
Right now, during retirement, DW and I are holding about 5% cash in a savings account and 95% VTSAX, because
our time horizon for investing is 40+ years!
Thinking of the accumulation phase and the withdrawal phase of retirement as two discrete things makes no sense to me. When someone starts saving and investing at, say, age 25, even if he's only planning on working 10 years and ERing at age 35, from the beginning he needs to be thinking about the fact that the money he's saving may need to sustain him and his family for 70+ years. In that case, IMO, the only rational choice is to invest in TSM.
I'm 50 years old, stopped working a little over a year ago and am planning on a 40+ year retirement. During the accumulation phase my wife and I always held 100% equities. I absolutely could care less about volatility. The dollar value of each share of VTSAX that I own does not affect me in any way, except when I sell shares. Obviously, when share prices drop significantly, we will be flexible and try to minimize the number of shares we sell for a couple of years, hustle a little bit, maybe make some money, maybe come up with some creative ways to spend less while still enjoying a high standard of living, but we're not going to panic.
I've watched the share prices of the equities I was holding plummet 3 times in my life: 1987, 2000 and 2008. The first time, I was young, and didn't know any better, so I sold all my stocks after the market crashed in October of '87. After that, I learned, and in 2000 and 2008, even though there was a lot more money in my accounts, I didn't sell anything, and a few years later my account balances were 2-3x what they had been before the crashes. Obviously, the fact that I kept buying stocks during that time, helped a lot.
I agree with ARS that how conservative you are in retirement depends on how much money you've got saved. If you've got way more than you need, then I guess it might make sense for some people to dial back their portfolios to be less volatile and try to preserve what they've got as much as possible. For many of us, though, ER is more of a continuation of the accumulation phase. Many of us will either make money and/or find creative ways to live on less during the early years of our retirements, in hopes that our 100% stock portfolios will continue to grow, even without our continuing to dump our paychecks into them.
Recently, I had my free investment consultation from Personal Capital. The investment advisor was like, "So, when you're 90 years old, your portfolio is still going to be 100% stocks?" My answer was, "Yes." He said, "That would be really risky!"
I told him, "I'm sorry, but I disagree." What risk could there be to my portfolio being 100% equities when I'm 90+ years old? If the stock market drops 50%, so what? I've still got the other 50% of my money, which will be more than enough to continue to draw 3-4% of the starting amount/year, or more, until we die.
All the charts from Tyler's site I've looked at in this thread only go back to 1972, so it's basically just one 40+ year period. Using FIREcalc and cFIREsim, we can look back at ~100 forty year periods and analyze how various AA's of bonds, stocks and cash would've performed. I trust those numbers more than just one 40 year period for GB.