But you're not discovering anything valuable because there may not be a person on the other end of a trade. You're just learning about the chaotic boundaries of the trading algorithm.
No, your interpretation is incorrect, and that's not how this works at all.
> There may not be a person on the other end of the trade
uh... what? If the executed order fills, then there was someone on the other side of the trade.
Anyways, by providing liquidity in any market as a market maker, you are effectively aiding in the overall process of price discovery. HFT shops are generally market makers, although other strategies are also possible depending on how the operation intends to generate alpha. For HFT MMs, they pretty much only make money by clipping spread, i.e. submitting dual buy and sell orders at the midprice with the expectation that they will make the (ask-bid)/2 on average. They then cancel these orders as the orderbook's structure changes and as prices and markets move, resubmitting at "better" (more favorable) levels.
It doesn't matter if people are buying or selling or both. HFT MMs provide a valuable service to financial market participants - if participating counterparties submit orders and cross a HFTs latest uncancelled order, it will fill, allowing market participants to quickly gain or lose exposure to their security or instrument of choice.
There's no magic here and you seem really confused about the underlying dynamics of trading and market microstructure.
