AFAIU the service HFT forms provide to the market is liquidity. Basically allowing you to sell stocks/options as soon as you feel like it.
In turn that leads to more efficient markets since prices converge to their "correct" value faster.
In turn that leads to more efficient markets since prices converge to their "correct" value faster.
The societal value of either is debatable all the same, mind you. It's more that wherever you have markets, you have money-making opportunities that can be leveraged, and therefore are.
Sure, Jane Street probably isn’t the fastest in the business, but I wouldn’t be surprised if they’ve got FPGAs or ASICs, dedicated high speed pipes to shave off milliseconds of latency, things like that.