In my opinion, assessment tools have a very bad impact.
If you are to decide and let a tool decide on your behalf instead, your people will get a bad impression, especially if the tool comes from other firms.
On the other hand, if you really need a tool to identify possible leaders in your organization …
Example: a tool deciding a person could get blocked in decisional environments. Try to guess? That person did practice “extreme sports”, i.e, he/she would have been dead had that been true. Nonetheless, he/she experienced problems in that occasion.