OTO removes the gap between getting filled and getting protected. The child order does not exist in the market until the parent executes, so you cannot accidentally leave a naked stop working on a position you never took.
It is the building block of the bracket-order and of otoco-order structures used by almost every retail platform.
Example: buy 200 shares at 45.00 (parent), which triggers a sell stop at 44.00 (child). If the entry never fills, no stop exists. If it fills at 45.00, your risk is defined at $200 the instant you are long, with no window where a fast move can hurt you before you react.
Related: otoco-order, conditional-order, bracket-order, oco-order