Do you give explanations when they are needed?

If I'm asked, sure. But other than that I'll just assume they understand where I'm coming from.

It depends on the person and the situation. A child will always get an explanation to learn why. I never liked " because I said so!"
In my life, people get explanations if it involves them to a great degree. Sometimes, it's personal and nobody's business. Still, if asked with respect, I will most likely do my best to explain.

Why wouldn't I?

Sometimes, yes

If required.

Only if they are needed and only if it's worth it.

Usually

Not anymore