If a firm is able to consistently get to all the other exchanges first, they can shave pennies off of a large percent of orders. That's a pretty big downside for everyone that trades.

They get accurate prices to the market faster, but only by a millisecond or so. That's a miniscule upside.

How is the bad not a thousand times the good?

Except for those who have their pensions stored in Renaissance's own pension fund, hah!