There are a number of drawbacks to using the Section 72(t) method of withdrawals. First, regardless of the method used, the process must continue for a minimum of five years or until age 59 1/2, whichever occurs later in time. 

Start at age 58, and you must continue until age 63. Start at age 50, and you must continue until age 59 1/2. If withdrawals are made from multiple IRAs, the five-year period runs separately for each IRA based on the date withdrawals started. This, obviously, can result in a lot of paperwork.

Second, if you make a simple math error in computing the exact amount of the withdrawal, if you stop the withdrawals too early, or if you change the calculation method, then all withdrawals up to that point are subject to the 10% premature distribution excise tax. And if that isn't enough, the IRS will also assess an additional penalty for failure to pay that amount in prior tax years.

Third, the life expectancy method too often fails to provide the needed income to the recipient anyway. To increase the amount, the person must use one of the other two methods and/or withdrawals from multiple IRAs. The "reasonable interest rate" that must be used in these methods, while resulting in a higher withdrawal amount, can be challenged by the IRS. 

Thus, it's a rate that must be selected with extreme care. Additionally, the calculations involved in the amortization and annuity methods may be beyond the capability of most folks. In short, the potential for error and subsequent IRS penalties with these two methods is large.

To be safe, those who wish to use Section 72(t) withdrawals should engage a professional skilled in the computations of all three methods. In addition, that professional should provide the account owner a letter specifying in detail the calculation method used. 

The letter should also specifically express an opinion that the calculations comply fully with the requirements specified in the IRC and by the IRS. That way, there's someone for you to point your finger at if everything blows up and the IRS comes a-callin'. 

Things are just much safer that way.