If you describe something as unnecessary, you mean that it is not needed or does not have to be done.
双语例句
例： The slaughter of whales is unnecessary and inhuman.
屠杀鲸鱼既不必要，也不人道。
例： She explained that it is quite unnecessary to hurt a patient.
她解释说根本没有必要让病人承受痛苦。
例： Don't take any unnecessary risks.
不要冒任何不必要的风险。