What is the difference between It's necessary and it's needed ?Feel free to just provide example sentences.

In absolute terms, the difference between "needed" and "necessary" is that "needed" is the intransitive form of the verb "to need". It is used in sentences where the source of need is unspecified since it is intransitive, in other words, "needed (by someone or by something)". "Necessary" is an adjective, so there is no nuance of someone/or something needing something. Both "necessary" and "needed" tend to be written or used in more formal speech, while "need" in its transitive form is more commonly used in spoken language. **However** sometimes sentences become very long if you have to use the transitive form of a verb and it is easier/shorter to use something like "needed" or "necessary" -- see the last example below.

In general, it is like the difference between 必要 and いる. However, some sentences would sound weird (a little) depending on the situation.

The planet needs your help.
The planet is in danger. Your help is necessary.
The planet is in danger. Your help is needed.

You need a ticket to get into this show.
A ticket is necessary to get into this show.
A ticket is needed to get into this show.

You need to be able to pay attention to detail if you work in the medical professions.
People working in the medical professions need to pay attention to detail.
Attention to detail is needed in the medical professions.
Attention to detail is necessary in the medical professions.

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