I don't understand the logic with employers dropping warnings like that. I knew ~2mo before my employer announced layoffs and it caused much unnecessary anxiety in my life.
I don't have a conclusive answer, but I'd want to know I think & respect companies that have the bravery to be up front.
As an IC, the day it happened and the weeks after it happened were tough, but I knew if I was the one impacted and my job was 'safe' for the time being.
As an EM, I knew months in advance, but I had no idea if I would be on the list. This caused months of stress while I planned for promotions and projects for people that might not (and eventually weren't) there after the rif.
Ripping off the band aid is much more human than telling people "sometime in the next 12 mo we may or may not fire a large portion of you, so please keep giving your 100%"
This gives the impacted people plenty of notice and time to look for new opportunities.
Now they have 80% of the company trying to leave.