... the immediate annuity could increase the amount that one could "safely" withdraw out of a retirement portfolio. Or on the flip side, the immediate annuity could increase the portfolio survivability for a given withdrawal rate.
This is all true. There are three downsides:
1. The company may go belly up, leaving you with nothing.
2. Your heirs get nothing.
3. You lose access to the money.
All three of these suggest not putting more than half, but many say
1/4th, or one's egg into SPIA; and diversifying risk by putting that
amount with more than one company.
So far, I've SPIA'ed about 7% of my egg (it was the amount sitting
in an after-tax annuity that I didn't like). I also annuitized part of a
TIAA-CREF retirement account (also about 6-7% of egg) because that
made me qualify for life-time free health insurance (hard to argue
with that one).
There was also an interesting paper FPA Journal paper recently
cited, that outlined a strategy of annuitizing WHEN a person's egg
got small enough to just barely afford a SPIA that would cover their
income requirements - "Modern Portfolio Decumulation: A New
Strategy for Managing Retirement Income". Hoping of course
that that never comes to pass !