needless waste/worry/suffering 不必要的浪费/担心/痛苦

Smoke alarms could have prevented these needless deaths. 烟雾报警器本可以避免这些不必要的死亡。

Needless to say, I was very upset about the whole thing. 不用说，我对整件事感到很不安。

These trees were needlessly cut down. 砍倒这些树是没有必要的。