There was a post some years ago that circulated these boards written by an ex manager in Cisco. His description was really a good and informative.
From my memory, it goes like this. Several weeks before earnings call/announcements, higher management decides about numbers that need to be slashed. Then they make lists.. They look into people working on projects that are going to be slashed, for example. In this case, it doesn't matter how good or bad you are, it is about project you're working on. But as we know, sometimes people that work on important projects are also let go. Obviously, there are other criteria involved, and they rank people by other metrics.
Once the lists are made, they go through legal to determine if some of those on the lists are from protected categories. Once these guys give a blessing, lists are final.
Now, important part to understand is that your manager isn't included in making those lists. Nobody asks them for their input. They only hear about it once the decision is made and then they go to some training how to deliver the news to impacted employee.
When it comes to those additional criteria, it can be the question if you met expectations for your pay grade during those performance talks with your manager. Then another criteria, and I was really surprised by it when I got such information is the IPF that you received last time. It was used as some kind of stack ranking metric. I thought that would be illegal, but it is probably something they can officially hide.
In this sense, your manager can affect your fate in LRs.
After learning all that, I noticed how my managers were acting and I figured what they were doing. If they want to keep someone, they put them on a good project. If they don't, they consistently put these guys on projects with the least importance or, in other cases, risky projects with a great chance of failure.