I think employee self evaluations provide additional data into an otherwise primarily subjective analysis. As a manager, if I get a self-eval that is inline with what I assumed they would say, I would structure my verbal interactions in the performance review/feedback session a certain way. If I get a self-eval that is completely out of line with what I believe the employee is rated at plus I have 360 feedback from peers or other examples that conflict with the employees self-eval, then I can structure the performance review/feedback session to line up the discrepancies. Once lined up, I can challenge the employee help explain the differences and help them correct my incorrect assessment or more likely, assist the employee in seeing how they are not interpreting clues and feedback correctly.
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