Just as investment industry behemoth Vanguard Group Inc. recently rolled out its new investment platform combining an automated and live-adviser experience with $17 billion in client money under management, regulators were warning about the growing ranks of robo-advisers.

Vanguard's Personal Advisor Services offers automated portfolio management, but with access to a financial planner via phone or videoconference for clients with a minimum of $50,000.

Fidelity, meanwhile, has a referral relationship with robo-adviser Betterment, and Schwab offers its own platform, Schwab Intelligent Portfolios. That's in addition to more than a dozen independent players, many backed by venture capital, including Betterment and Wealthfront.

For their part, regulators stuck a flag in the ground, issuing an investor alert about online financial tools in general, not just robo-advisers.

Here are the key issues the regulators raised that most pertain to retirement savers.

Know the program's limits. A computer algorithm, whether it's used by a consumer directly or by an adviser, might only be programmed to consider a tight range of interest rate fluctuations over time or only a certain brand of investment products.

Watch yourself. The answers you give to a tool's initial questions about your situation and risk tolerance can greatly affect the investment recommendations and might lump you into an investment path that isn't truly reflective of all your goals. In other words, it might ask about your long-term savings without also asking whether a portion of that might be earmarked for a child's college costs.

"You could argue that when you're sitting down with a professional it's the same concern, though perhaps there is a bit more detailed of a conversation" with a live adviser, said Lori Schock, a director with the SEC.

That conversation is still bogged down in an ongoing Labor Department proposal to require elevated standards of care for all advice pertaining to retirement accounts.

But it does draw attention to the caveats, both of live and automated investment advice: When so many retirement savers have virtually complete discretion over large lump sums, the potential pitfalls are deep.

As are the implications. American investors now actively control nearly 60 percent of the $24.7 trillion U.S. retirement market.

Janet Kidd Stewart writes for the Chicago Tribune.