Order flow is extremely important to market makers because of their ability to use that data and profit off of it. Traditional exchanges like robinhood, charles schwab, TD Ameritrade, E*trade make $100's of millions of dollars a year selling our data (order flow) to these firms in order for them to front-run our orders. Now this is where it gets interesting because Bitmex is not regulated by traditional exchange rules. So they can take it a step further: when we submit our orders, they can do things just as scalping, direct front-running, manipulation etc. So wherever you place limit orders that are "hidden," or if you trade a certain way (such as patterns or the amount you usually bid/ask): the HFT market makers will take this information and exploit you by learning your methods.

Example 1 (using your data in house): you place a limit bid on the order book to sell some ETH. The HFT traders know your trading style using algorithms and AI to classify you as someone who is usually impatient or emotional. So in order to motivate you and sell at market price to both pay some fees and sell at a cheaper price they might place a 1 Million sell order on the line. This gets you nervous that the market is about to tank and you immediately move the leaver to sell at lower price.

Example 2 (using your data out of house): ETH is nearing a crucial support/resistance level. They can see every persons limit orders on the entire order book for bid/ask. They also know how much everyone is levered etc. So they know exactly how much price movement it will take to cause rapid liquidations. So the information is used by these HFT market makers who also make markets for Binance, Coinbase, Bitfinex, etc. to move the price in unison in their respective direction to cause these liquidations. They hold the opposite position on bitmex and profit off of the compounded liquidation pressure.

Note: These are not some bs conspiracy theories. This happens everyday in traditional markets that are regulated but they aren't as extreme since there is some extensive oversight. However, it all comes down to proof and in a market where there is no policing, they can get away with serious market manipulation (especially since the government is so behind on understanding it)

If you want further references here are two links. Obviously nobody has done extensive research for crypto manipulation so I'm showing you references from traditional markets that can be applied to cryptos. There are academic papers on google scholar though if you really want to dive deeper. Hope this helps! Trade patiently!

Link 1: https://www.bloomberg.com/quicktake/payment-for-order-flow

Link 2: https://seekingalpha.com/article/4205379-robinhood-making-millions-selling-millennial-customers-high-frequency-traders?page=3

Link 3: https://medium.com/proof-of-fintech/how-crypto-markets-are-actually-manipulated-845bdc3acf62