These need to be evaluated to determine the adequacy of a retirement fund. Non tax-preferred investments might produce a higher return and a larger retirement. There is no guarantee that the current level of safety can be maintained in the face of an increasingly older average population. Just as return on investment and length of investment are important in determining the amount of capital accumulation, they are important factors to evaluate in capital withdrawal. Unless expenditures exceed this level, the estate will grow, rather than diminish.
Planning is expensive.
Lack of planning is more expensive. Also, to the degree that you do work that does not require professional expertise, it frees the professional to give better advice and reduces your cost.