The economic value is providing better prices for people buying stocks. (If they didn't provide better prices, no one would trade with them, they'd trade with o

The economic value is providing better prices for people buying stocks. (If they didn't provide better prices, no one would trade with them, they'd trade with other market participants, because those are the rules of the exchange: you get a better price when it's offered.) The economic value is found by removing overhead on the order of around a cent (or less) per share per transaction, which starts very very small but adds up quickly. (There's also a huge latency-game going on there because you can't price more accurately than one cent, due to regulations, which is another inefficiency.)