This instance of のに is opposite from my expectations


I have this sentence in one of my JLPT practise books:

> 電子{でんし}レンジは冷{さ}めた料理{りょうり}を温{あたた}める **のに** 重宝{ちょうほう}だ。

I thought `のに` meant something like "in spite of". So, to me, this sentence
seems to be saying that a microwave oven is convenient (or a "precious
treasure") _in spite_ of the fact that it warms cold food.

... but, isn't that exactly what a microwave oven is supposed to do? Shouldn't
the sentence be something more like:

> 電子{でんし}レンジは冷{さ}めた料理{りょうり}を温{あたた}める **ので** 重宝{ちょうほう}だ。

Is this a typo, or is `のに` used in another way that make sense here?




のに can have several meanings, "despite" being the most common one. But it can
also mean "in order to" (~のため）. Here are some examples (taken from
[here](http://www.jgram.org/pages/viewOne.php?tagE=noni-2)):

> パスポートは海外旅行に行くのに必要です。  
>  A passport is necessary to travel abroad.
>
> 電子レンジは冷めた料理を温めるのに重宝だ。  
>  A microwave is handy to heat up cold food.




のに can have several meanings, "despite" being the most common one. But it can
also mean "in order to" (~のため）. Here are some examples (taken from
[here](http://www.jgram.org/pages/viewOne.php?tagE=noni-2)):

> パスポートは海外旅行に行くのに必要です。  
>  A passport is necessary to travel abroad.
>
> 電子レンジは冷めた料理を温めるのに重宝だ。  
>  A microwave is handy to heat up cold food.

