The author is a critic of continuous limit-order book markets for what seems to be a different reason: as the interval at which things trade constricts, correlations can break down between things that should be priced 1:1.<p>His best example is ES and SPY, two different ways to trade the S&amp;P500.<p>There&#x27;s a straightforward high-frequency arbitrage strategy to deploy against that problem: if ES or SPY is &quot;mispriced&quot;, trade in offsetting amounts, in the expectation that the correlation will be restored (as it must eventually be). In Budish&#x27;s view, this trading is a needless cost that doesn&#x27;t improve price discovery.<p>I&#x27;ll just say, that&#x27;s not IEX&#x27;s argument against HFT.