There's a well-known phenomenon whereby narcissism and self-evaluation is generally related to positive mood. It's part of an overall positive tint.
So one interpretation of this is that people who tend to be optimistic also tend to just feel better in general, for whatever reason.
It's not clear to me these "benefits" would transfer to all scenarios, nor is it really clear that it's about insight in general in the way people usually understand it.
I was thinking of benefits like being able to better learn to overcome your own limitations or put yourself in situations where you’re likely to succeed.
Near-zero percent of people is any close to knowing themselves. Begin able to assess your expertise and capability in particular area is a useful skill yet it doesn't mean knowing your actual self. The first step toward actually knowing yourself is observing your own feelings, thoughts and behavioral patterns "from a distance" breaking free from the habit of taking them too seriously.
