1) It reduces the bid/ask spread. There isn't just one price for a stock, there are two. The price at which you can buy and the price at which you can sell. The price at which you can sell is lower. So when you buy a share of stock you are immediately down a little bit. This amount is called the spread. By automating firms can reduce this spread which does the opposite of what your intuition told you. It will bring buy prices down slightly and sell prices up slightly.
2) It helps make sure that prices are as accurate and up to date as possible. When you go to buy a share of $GOOG you probably aren't really sure if it should cost 775.40 or 775.45 or 775.50. You just figure it's a good company and likely to go up in the future. But because there are all these firms working really hard and acting really fast you can be pretty confident that whatever price you buy at at any given time contains the total available knowledge currently available in the world about Google's future potential.
1) It reduces the bid/ask spread. There isn't just one price for a stock, there are two. The price at which you can buy and the price at which you can sell. The price at which you can sell is lower. So when you buy a share of stock you are immediately down a little bit. This amount is called the spread. By automating firms can reduce this spread which does the opposite of what your intuition told you. It will bring buy prices down slightly and sell prices up slightly.
2) It helps make sure that prices are as accurate and up to date as possible. When you go to buy a share of $GOOG you probably aren't really sure if it should cost 775.40 or 775.45 or 775.50. You just figure it's a good company and likely to go up in the future. But because there are all these firms working really hard and acting really fast you can be pretty confident that whatever price you buy at at any given time contains the total available knowledge currently available in the world about Google's future potential.