This is a crazy approach. It signals the company is on trouble so the first to go will be your best, who all have lots of options. Anyone half decent will immediately start risk diversification by looking for other opportunities. Meanwhile nothing will get done by anybody and in the end your left with the dregs.
Far better for everyone involved to do it quick rather than perfect. Those getting let go shouldn't see it coming and those staying shouldn't find out before it's all been done.
The tell in advance approach is common place in countries with strong unions. The company might need to announce layoffs half a year in advance of the actual layoffs.
In effect noone will lose their job quickly unless there is a bankruptcy.
There is probably way less confusion in that way since you know that security guards wont escort you out any minute ...
Far better for everyone involved to do it quick rather than perfect. Those getting let go shouldn't see it coming and those staying shouldn't find out before it's all been done.