Talent Review/Succession Planning - Does anyone have employees complete a self-assessment on the same potential criteria as managers? The thought here is it would give leaders an understanding of where the employee views their potential.

If you google "Research-based accuracy of self assessments" you'll find that there is a lot of evidence to show that self assessments are really inaccurate.

Some interesting research done by Bob Eichinger and Mike Lombardo established that a great way to identify high potentials was to ask them to rate themselves on pretty much anything. High potentials would consistently "UNDER RATE" themselves because they knew what they didn't know.

One of the clearest attributes of a high potential is learning agility. People who are great learners see the "space" they can fill with new knowledge and insight.

If you ask someone to assess themselves, and then that rating is shared with their manager, there are only so many possible outcomes.

1. They agree: So not much value in that, no new information.
2. Employee higher than manager: Definitely a difficult conversation, very likely to trigger a defensive (fight, flight or freeze) response. You could avoid the conversation, but as the employee I'd ask why I bothered to fill it in if you weren't going to talk to me about it.
3. Employee lower than manager: Probably a high potential :) that just cast doubt in the manager's mind as to whether they are actually a high potential if they don't see it.

There just aren't any real wins from doing (that I can see), but I'd be really interested to see how it turned out.

Yes, and I find that it's super helpful to do so in order to see where there might be a disconnect or miscommunication, and also as a way to gauge self-awareness and better understand someone's potential, career trajectory, etc.