Story time :
I remember having formal continuous objective KPI based reviews.
I did incredibly well until my female boss took a severe dislike to me and tried to get me fired. (I effectively started doing hrr job better than she did and she got threatened.)
When called out by out CTO I pulled out a copy of all of my reviews and showed him.
About a week later I was called into his office with my boss who managed to force out a few tears and convince the CTO that I had effectively bullied her in my reviews to give me good marks. The CTO consoled her and effectively threw away the documented reviews.
Fortunately I argued to be moved to a different team and I was put on probation for three months.
Luckily I performed well and impressed my new boss who wasn't insane.
Moral of the story is even if you have a documented history of good KPI reviews you are screwed if your boss doesn't like you. Performance reviews are there to cover the companies arse.
+1
My experience has taught me that as long as you have managers that are reasonable and understand what development is about, assessments should not be a problem even if there are no specific KPIs in place. The problem starts with people who either have an issue with certain individuals or unqualified and incompetent managers. They can always make you life a living hell with HR et al.