A hard stop is an instruction sitting in the market. Once placed, it executes without you: no hesitation, no renegotiation, no waiting for one more candle.
The trade-off is honest and worth stating. A resting stop guarantees the exit is attempted but not the price - a stop-order becomes a market order when triggered, so in a fast tape you get whatever is there, which is what stop-slippage measures. It is also visible to the exchange, which fuels the perennial stop-hunt complaint. In liquid instruments the visibility argument is mostly folklore; in thin small caps and off-hours futures it is not.
For anyone who has ever widened a stop in the moment, the hard stop is the correct default. The discipline cost of a mental-stop is paid in the exact trades you cannot afford, because those are the ones where the temptation to wait is strongest.
Related: mental-stop, stop-slippage, catastrophic-stop, stop-distance