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What are the gains from more liquidity in ETF for small investors?
ETFs are both liquid (benefits active traders) and a simple way for people to invest in funds even if they don't have the minimum balance needed to invest in a mutual fund (EDIT: in which purchases are resolved at the end of the trading day). One big difference between ETFs and mutual funds is that you must buy ETFs in whole units, whereas you can add $100 to a mutual fund and the fund will determine -- usually to 4 decimal places -- how many shares you've purchased.