Buying a lot of shares at once. I wrote a blog post explaining how to not trade with HFTs if you don't want to:

http://www.chrisstucchio.com/blog/2014/how_to_not_get_ripped...

Quoth a trader: "Let me tell you this as trader with 15 years direct bank and hedge fund execution experience. Your suggestion of using such algorithms would result in me never getting filled even remotely close to where I wanted to get filled."

tl;dr; He wants to buy 10,000 shares right now and HFTs are the only ones offering that.

So its good for the trader who wants to do that. Is there any benefits to the market overall that he wants to do that?

Edit: Can someone explain to me why I am being down voted from asking a question? It seems like every time I get into a discussion with yummyfajitas I am being down voted?

Allowing a trader to make large trades makes price discovery happen faster and more accurately. I've written a more detailed explanation on my blog - read HFT apology 1 and 2.

http://www.chrisstucchio.com/blog/tags/high%20frequency%20tr...

As for the downvotes, I lead a small cult of traders, rationalists and scala programmers - tptacek is my #2 sycophant.

So again the trader not the market/society.

Whats the benefit outside the stock market to society in general? I.e. how is HFT a net profit to other than those involved in HFT?

You are asking people to be specific, can you you?

The tutorials I linked to address your questions in detail.

You must be able to give examples.

An example is provided in part 2 of the tutorial. Are you demanding I copy&paste it here?

Yes please

o.O

Amusingly: this comment was downvoted 8 minutes after I posted it, despite the thread being 6 days off the front page. :)

Yes: limit orders provide liquidity, and market orders sap it.