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Why is tax loss harvesting helpful for passive investing?
Your assertion that you will not be selling anything is at odds with the idea that you will be doing tax loss harvesting.  Tax loss harvesting always involves some selling (you sell stocks that have fallen in price and lock in the capital losses, which gives you a break on your taxes).  If you absolutely prohibit your advisor from selling, then you will not be able to do tax loss harvesting (in that case, why are you using an advisor at all?). Tax loss harvesting has nothing to do with your horizon nor the active/passive difference, really. As a practical matter, a good tax loss harvesting plan involves mechanically selling losers and immediately putting the money in another stock with more-or-less similar risk so your portfolio doesn't change much.  In this way you get a stable portfolio that performs just like a static portfolio but gives you a tax benefit each year.  The IRS officially prohibits this practice via the "wash sale rule" that says you can't buy a substantially identical asset within a short period of time.  However, though two stocks have similar risk, they are not generally substantially similar in a legal sense, so the IRS can't really beat you in court and they don't try.  Basically you can't just buy the same stock again. The roboadvisor is advertising that they will perform this service, keeping your portfolio pretty much static in terms of risk, in such a way that your tax benefit is maximized and you don't run afoul of the IRS.