The に particle outside of location and direction

Question

I am well aware of how に works compared to で and how to use it in various situations. I still have trouble with a few uses that keep popping up, as they don't seem to gel with my current understanding.

For example それは体に悪いです

I see に as a particle that shows 2 things,

1. A particle that denotes movement form larger area to settle in somewhere specific. It is used with verbs like 住む　勤める　and 乗る for this reason.

2. A particle that effectively turns the noun or quasi adjective into an adverbial phrase. Used with 静かにしてください　ハンバーガーにします etc to show the way you will "do" for want of a better word. It also is used in passive phrases to show that it was by someone else's motions that something happened, like "田中さんにビールが飲まれた"

So my question is, how do I understand phrases like 体にいいです or 会社に行くのにバスと電車を使っている Is that a third usage meaning "for"?

BONUS QUESTION:Are there any other usages of に I should look out for?

Answer 1

There is another usage for the particle に: that of an indirect object, and similarly it is used in the same way as the preposition "to" in English. Look at the following example:

I gave my mother a gift.
私は母におくりものをあげました。

In this case "mother" is an indirect object. In other words, she is at the receiving end of the action. Often times there is an invisible "to" or "for" that can be applied to an indirect object. Look at a second example:

I bought a new toy for my sister.
私は妹に新しいおもちゃを買いました。

In this case "sister" is the object of the preposition "for", but it can also be thought of as an indirect object, because the "for" could be omitted and the sentence is "I bought my sister a new toy".

The particle に performs both of these functions, which are more or less interchangeable in English. So "それは体に悪い" means "That is bad for the body."