I studied up on this a fair amount, and sequence of return risk is huge the few years just before reaching FI and the ~5-10 years after FI. I wrote something up in a previous thread.
http://forum.mrmoneymustache.com/investor-alley/100-stocks-in-the-accumulation-phase/msg1177820/#msg1177820Basically, if the market takes a 2-3 year slide in the 2-3 years before you reach FI (say down ~3-5% per year for a max drawdown of 10%) you'd have to work extra if you were 100% stocks. If you switch your AA to something much more conservative, you'd maybe have to work an additional few months or quite possibly no additional.
Example: You have $800k invested in 100% S&P500, and you need $1MM invested to give you $40k per year for FIRE. Let's say you can add $50k per year from job earnings. We'll make it easy and make the market give us equal % returns over 2 years to give us $1MM total (which would be 5.6% per year). Seems feasible right?
Conversely, the market starts to go down as the fed increases lending rates and the global economy doesn't do quite as well with higher borrowing rates. In the first year the S&P500 drops 5%. Now you have $810k invested (= $800k original minus $40k loss plus $50k earnings addition). Then the year after that, the market drops another 5%, which gives you $819.5k. At this point, you might say "screw it, the market has gone down the past 2 years and is ready to go back up so I'll just retire on a ~4.9% WR". Or, more likely, you'll work an additional 1-2 years to get to $1MM.
Alternatively, you could go 50/50 stocks/bonds over the next 2 years and hope to break even (0% returns over the 2 year period). Which would give you $900k invested ($100k addition from earnings over 2 years), which would be a ~4.4% WR. Or, you could work another 6 months (maxing out all tax deferred accounts during this time) get up to ~$950k just with new additions, FIRE, and see where the market goes from there.
The numbers don't lie, if you are near FIRE, it is in your best interest to have your AA be closer to 50/50 than 100/0. If you are already FI, and are still working OMY, then I'd say keep your AA where you have it. Anyone planning a 3% WR with FIRE could easily keep their allocation closer to 100% stocks.