对他为什么这么做妄加猜测毫无用处。

It is useless to speculate why he did it.

《牛津词典》

然而，这样的水对提高身体机能毫无用处，因为只有通过肺部才能将氧气吸入血液，从而被肌肉吸收。

Such water would be useless in improving physical performance, however, since the only way to get oxygen into the bloodstream so that it can be absorbed by the muscles is through the lungs.

youdao

许多评论家声称，在教育中心教授的一些课程只是在浪费时间，对学生毫无用处。

Many critics claim that some subjects taught in educational centres are just wasting time and are not useful to the student.

youdao

Doing incrementation, pretty useless; right?

做增量运算，相当无用的，对不？

哈佛公开课 - 计算机科学课程节选