The basic benefit of tax deferral on investment growth is relatively straightforward: by not paying taxes, money that would have otherwise gone to the government instead can remain invested for future growth. To the extent the money will ever be spent, the taxes must eventually be paid, but as long as additional growth can be generated in the meantime, that is a value for the investor. As a result, investors often focus on deferring capital gains, and reducing the rate of portfolio turnover.
Yet a deeper look at the actual economic value of tax deferral reveals that most of the benefit is actually lost with even low levels of turnover. An investment that changes just once a decade actually forfeits more than half of the tax deferral benefits over the span of 30 years, and for a portfolio with dividends as well, a mere 10% turnover forfeits more than 2/3rds of the tax deferral value. In a lower return environment, the true tax deferral benefit of extending the average holding period of an investment from 2 years to 5 years - chopping the portfolio turnover rate from 50% down to 20% - is actually less than 5 basis points, which can be made up in the blink of an eye through a lower cost investment change or a mere day's worth of relative returns (not to mention weeks, months, or years)!
In turn, these results suggest that in the end, investors may be grossly underestimating the damage that's done by having any portfolio turnover, and grossly overestimating the value of trying to add several years to the average holding period of an investment. Of course, high turnover investing has other costs as well, and the results don't necessarily mean that rapid trading will be fruitful. Nonetheless, the limited value of tax deferral even for an investor with a decade-long average holding period suggests that investors should be highly cautious not to sacrifice prudent investment decisions upon the altar of low-turnover tax efficiency, and that it may even be time to reconsider asset location decisions and whether equities should be held in tax-deferred accounts instead.