Retirement Spending Projections

I have never liked the order that Quicken chooses as far as when to tap a certain kind of account type.  It is one reason I just use the Life Time Planner as a "rough guess", since you can't control this order, and can certainly disagree on how it should be done.

Note that the order that one might use might not be to preserve the Roth as long as possible if the goal is to reduce the amount of tax paid in certain periods of time.

The advantage of the money in a Roth or a regular taxable account is that it isn't considered "income" as far as your taxes go.  So say you need $50,000 for your expenses.  If you took out say $30,000 from traditional IRAs/401K accounts and then covered the rest of the expenses with either Roth of regular taxable account funds then you would be paying tax on $30,000 instead of $50,000.

The point is that having such different accounts allows different "mixes" that Quicken would never be able to figure out what is best for any given person without having a way for the user to say which accounts they want to tap for what and at what time.

My example might not line up with exactly what you were asking, but the point is that the user has no control over this the Lifetime Planner has a set of very simple rules, take money from this account type first, then this type, ...

And it will certainly be wrong for a lot of people, and I can't tell you why they picked the rules they did.  I doubt anyone could.  But even if they could that really wouldn't change much, you would simply have a reason why they do it in a way you don't want.

But with all that being said yes if all I had was Roth IRAs and taxable accounts I probably would "mostly" tap the Roth IRAs last.

But note you are wrong about this statement
"then your only other income source would be taxable accounts and you cannot choose to not recognize income from taxable accounts."

You don't pay tax on money withdrawn from a taxable account.
First lets make sure we have our definitions in line.

Traditional IRA/401K/... tax deferred.
Roth IRA/Roth401K/ ... tax exempt
Savings,Checking,CDs,.../ "taxable"

For "tax deferred" you pay the tax when you withdraw the amount.

For both of the others types you pay the tax as the money goes into the account.
And in the case of the "taxable " that includes "interest/dividends", but in the case of the "tax exempt/Roth" accounts you don't pay taxes on the gains.

But in both cases "tax exempt" and "taxable" you don't pay tax on withdraws.

If I paid my expenses with $30,000 from my savings account, and $20,000 from my Roth IRA, to the IRS I would have an "income" of zero.

As I see it the main reasons I would delay withdrawing from a Roth over using my cash on hand would be first off that the gains in the Roth aren't taxed. And the second might be because it might be a bad time to sell off a given security.