They don't. That term has basically become an advertising slogan for IEX. HFT is great for retail investors because you trade cheaper and faster. Usually retai

They don't. That term has basically become an advertising slogan for IEX. HFT is great for retail investors because you trade cheaper and faster. Usually retail investors get price improvement over the market since HFT brokerages compete for retail flow. HFT is bad for institutional investors who don't want to invest in sophisticated execution since the market reacts very quickly to large orders. Institutional investors include firms like Vanguard or firms that greatly inform price discovery, so it's worth thinking about both sides of the market and not just optimizing for best retail execution. IEX is by and for large institutional investors. IEX's delay doesn't apply to one (multiple?) of their hidden/protected order types, which allows larger orders resting on the book to avoid market impact and execution at 'bad' prices as these orders can move away from the top of the book in 'unfavorable' market conditions.