It turns out “do-it-yourself” investing is not all that it’s cracked up to be.

Employees saving for retirement in workplace 401(k) plans are increasingly eager (or willing) to autopilot their allocation and portfolio management decisions.

Vanguard reports that among the more than 8,500 retirement plans it administers, with more than 4.6 million participants, usage of target date funds, balanced funds or managed account services has tripled in the decade. This explosive growth has taken place since Washington gave its blessing for plans to use target date funds (TDF) as the “default” investment.

More than half of workers now rely on some form of portfolio allocation advice, with the vast majority being a TDF. Vanguard expects nearly 75 percent of investors will be leaning on professional advice within the next three years.

An off-the-rack portfolio allocation that relies on just one retirement date is no one’s definition of optimal, but that’s a bit of a faulty premise. Target date funds were never designed to be perfect, but rather to address costly participant missteps such as sitting in cash, holding way too much company stock, and not systematically re-balancing their portfolio.

“Optimal is popular among academics, but it is never achieved,” says Michael Guillemette, an academic at Texas Tech University’s Personal Financial Planning program, who co-authored a study on the utility of TDFs for unsophisticated investors.

“You want to get as close to optimal as possible and TDFs are step in that direction,” said Guillemette, who is also a certified financial planner.

Full content: CNBC