>Its about what the bulk of the trading is: robots trading with robots without any regard to the stocks they are trading. The big whales are the mutual funds and they have to execute their buy/sells using special techniques of spacing trades out to try to not show what they are up to. Otherwise the HFT spots it (and they usually do) and then front runs all of the trades, just skimming pennies off. What use are they ?

They can do the trade slightly faster, and according to the rules of the market, if you place an order to sell with a limit of $50 then someone willing to buy now for $50 beats someone willing to buy a second later for $51. If that's not what you wanted, you should have made the limit $51.

Maybe we need new order types, but that would set off a slew of complaints about additional complexity. And note that eliminating the sub-penny rule would put a lot of the front-runners out of business, since they'd only be making $.001 per share rather than $.01.