With all due respect it was a question about when you could take out the conversion principle. Not a strategy. There are many reasons to convert. An example, if your assets are currently below market value, moving them to a Roth, they get taxed at market rate (think bonds). When they mature, they mature at face value. Being in a Roth, there is no tax implication in that gain. If you just took them out of the IRA, yes there would be less initial tax due to the lower market value, but then you would get taxed on the gain when they mature. Some numbers to clarify. You withdraw from an IRA $100,000 face value in bonds, but their market value is $90,000. Drawing it out as an asset (not sell it and take the cash), you pay tax on $90,000. When the bond matures, it pays face value, so you have an additional tax liability on the $10,000 gain. Rolling it into a Roth, you eliminate that liability.
