With respect to reviews, 'differentiating performance' is being created via a kind of corporate transubstantiation move (analogous to the way the Catholic Eucharist turns wine into the blood of Christ). In this move they convert 'differentiating value of the role' into 'differentiating performance of the employee'.
They start by identifying those whose roles have less 'perceived value' (they know they could do without this or that role if they had to, that person is paid too much, and so on.), and then they convert that to 'substandard performance' through the magic of corporate double-speak. Finally, they back fill the review with lame explanations, justify the BE rating, and then force the employee to drink the nonsense.
Voila! The wine has become the blood of Christ!
It's patently unethical and they know it.