It's the intersection of two different models of the financial universe. The long-term investor has an interest in liquidity and a reasonable response time to

It's the intersection of two different models of the financial universe. The long-term investor has an interest in liquidity and a reasonable response time to market moving news. He's making decisions about a company based on expectations of the future. Typically, if his trade clears in 1 minute-- or even 1 day-- instead of 1 millisecond, there isn't that much in it except in some corner case situations. The short-term investor is mostly interested in reacting to the noise in the signal-- getting a few nanoseconds ahead of other sellers and positioning accordingly. If you have enough of a "we got the info first" edge, you don't have to have any real opinion of the companies you're investing in, or even a preference of long or short, you can systematically ride the signals. The justifications for ever-faster trading tend to break down as "more liquidity" and "less arbitrage", but we're not asking if the marginal increases in performance there are worth the costs-- both in the arms-race for faster market and informaion access, and in the impacts on market behaviour caused by large numbers of super-short-term investors throwing their inertia around tiny swings in the market.