Buyers and sellers of stock face a spread anyway. Quants make the spread smaller by arbitraging it. They are now so good at it that the profits are down to 20%

Buyers and sellers of stock face a spread anyway. Quants make the spread smaller by arbitraging it. They are now so good at it that the profits are down to 20% from what they were a few years ago. Mutual funds and other investors can now thus buy their stock with smaller spread, i.e. smaller 'salami slice' to give up.