The inessential has become perfectly essential.

用之物都变成了有用之才。

These changes may be inessential, but they are harmless.

这样的改变也许关紧要，但却不麻烦。

A sense of smell has long been regarded as something trivial and even inessential to humans (as opposed to other animals, such as dogs, who live by their noses).

长期以来，嗅觉一被认为人类微不足道的东西，甚关紧要的东西(与其他动物相反，比如狗，它们靠鼻子生活)。

I think this kind of thinking, the thinking that senior employment is inessential, is actually the seed of a major problem that could impact a lot of lives, especially the lives of people in developing countries.

我认为，这种想法，即认为老年人就业关紧要，实际上一个重大问题的根源，尤其影响到发展中国家人民生活。