Taking out travel insurance may seem an unnecessary expense, but it is a must.

旅游保险费用看起来似乎是没必要的，但却是必不可少的开支。

《柯林斯英汉双解大词典》

Perhaps that is because computers are less visibly polluting, or their use is not deemed, like air travel, to be frivolous and unnecessary.

或许，这是因为电脑的污染更加不易被察觉，或者其之使用不像航空飞行一样被认为是不重要且不必要的。

youdao

Tourism spawns unnecessary litter, when you travel you must think about the environmental impact.

旅游业产生了不必要的垃圾，要旅游同时一定要考虑到环保。

youdao

His lawyers argued in their appeal filing that since Pistorius was not considered a flight risk, the restrictions on his travel were unnecessary.

CNN: South Africa judge lifts travel ban on Oscar Pistorius

The athlete's lawyers argued in their appeal filing that since Pistorius was not considered a flight risk, the restrictions on his travel were unnecessary.

CNN: South Africa judge lifts travel ban on Oscar Pistorius

He advised people to avoid unnecessary journeys and to drive carefully if they do need to travel, allowing extra time for journeys.

BBC: Lincolnshire Police called to crashes amid ice and snow