You 'point something out' if you think it is important that the other person should know this. For example, if you see a mistake in a report, you should point this out to someone. This means that you draw someone's attention to it. It's like pointing your finger at something to draw attention to it. 'Mention' simply means to say or refer to something.

"To point out" is more specific than "to mention". If you are "pointing out" something than you are deliberately referring to it or hinting at it. But you can "mention" something - by chance or not - in the course of a conversation without highlighting it.