Just remember if you try and roll a traditional 401K into a ROTH IRA, you'll be socked with taxes. If you roll it into a traditional IRA, you won't. You'll only be taxed on the withdrawals from the traditional IRA as you make them.
Some may think it's better to pay all the taxes on it now, as taxes are not likely to ever decrease. Some may not. So do your homework before you move anything.
Now that I'm old enough that the RMD, Required Minimum Distribution, is forcing more income subject to tax than I need to live on, I'm wondering if it might have been better strategy to do the maximum IRA > Roth conversions years ago.
And pay the tax on the IRA withdrawal at that time, before the money within the IRA compounded to a larger number that is now taxable each year as forced withdrawal.
The mandatory RMD is based on forcing you to cash out your entire 401/IRA balance within your estimated remaining lifetime so the forced withdrawals - and the tax on them - become massive, later on.
I don't know how to calculate the alternatives for massive taxable IRA > Roth conversion before retiring, contrasted with IRA withdrawal years later with greater tax consequences. But good retirement planning software likely has this conversion scenario built into the calculations by now. (As I've mentioned I used QuickBooks planning software 25 years ago when I was forecasting if I could afford early retirement).
Like Bearsixty7 above, I relied on IRA withdrawal to supplement my relatively small pension and wife's income (she loved her part time job) until I reached SS age. By that time investments were doing well so I put off starting SS until 67.
There was also some gimmick where my wife's SS was related to mine, I don't remember the details. But as I recall she delayed starting her own SS until age 70, several years after retiring, so so check this out.
Events since that initial planning have exceeded the software forecast. So that planning, putting in all the alternatives and letting the software solve for the outcome of each possible scenario, was more than worthwhile. I don't know which modern software is best for this retirement forecasting. Does anybody have a favorite?