OTOCO is one-triggers-other plus oco-order: one submission defines the entire trade. Most platforms label it a bracket-order in the order ticket, though the underlying message structure is OTOCO.
It matters most for traders who cannot watch the screen. The exit logic lives at the broker or exchange, not in your head, and it survives a dropped internet connection.
Example: buy 1 futures contract at 5,000.00; on fill, submit a sell limit at 5,010.00 and a sell stop at 4,995.00. Ten ticks of risk against twenty of reward. If the target trades, the stop is pulled automatically, so you are never left short a contract you did not intend to have.
Related: one-triggers-other, oco-order, bracket-order, conditional-order