What 'HF'T teams do is high frequency trading, or rather low latency trading. You put offers in the book you feel comfortable trading at, and you are happy if y

What 'HF'T teams do is high frequency trading, or rather low latency trading. You put offers in the book you feel comfortable trading at, and you are happy if you trade at that price. If the market price stays static they pick up the spread on average. However, the reason they are so tight in the order book, is because if the market moves they're very quick to pull their offers and bids and move to a new price. HFT companies are providing liquidity in that situation. As long as you place a single order, it will get fulfilled. So to be clear, the HFT firm that places orders in the market want to trade those offers. They're comfortable placing those orders more competitively than your average punter because they can respond to market moving events quicker. Layering and spoofing is something different - you're placing orders in order to make people think you want to trade, but you don't. It's like asking me what's the difference between Al Gore offering you money to tackle climate change and a climate change denier offering you money to tackle climate change? Well one of them is clearly lying.