I would guess he is saying that if you have no other income, RMDs/withdrawals from tax deferred up to the standard deduction would have a 0% tax rate.
Aha! That must be it. I bought Pralana to get beyond those kind of mantras. I learned the devil is in the details.
At about 32 min into the youtube, Bill said that most people don't go into the weeds when it comes to Roth conversions, they use non-mathematical reasons, do not use optimization, just use marginal tax brackets. I like that. I think we make Roth conversion decisions too complicated. Long term - do you expect to be in a lower tax bracket when say, you turn 70 years old, then don't. Same or higher tax bracket, then convert. Remember at age 70 you will be getting Social Security (SS), maybe pension, and RMDs. Add those up. Using Pralana, see if your RMDs are greater then your needs, if so, convert.
I use an even simpler method: If Pralana's optimizer doesn't show more than 25% difference in eolv I don't convert. It's not that I wouldn't value the extra $ for less than that. But, rather, that giving up a definitive dollar now for a possible dollar later (based on unknown future tax brackets, tax policy, Medicare rules, health costs, SS, system shocks, and the variability of returns) requires a much bigger pay-off. I may regret this at age 80!
Jonathan's Law: Don't confuse the comfort of a definitive bar chart going forty years in the future with the real world being that comfortable going forty years into the future.