The Bogleheads' Guide to Investing

Vanguard offers their low-cost ETFs commission-free, eliminating the previously mentioned downside associated with having to pay commissions to buy and sell ETFs. When used properly, low-cost ETFs can certainly play an important role in a long-term investor’s buy-and-hold portfolio. On the other hand, investors are likely to shoot themselves in the foot if they plan to use ETFs as day trading or market timing vehicles.