The problem with advance warning is the employee who decides to sabotage in revenge.

For example, a company I knew in the 80s had a wholly owned subsidiary. It was losing money, so it was decided to close the subsidiary. Management decided that they'd be nice guys, and notified the subsidiary that it would be closed in 90 days and then everyone would be laid off.

90 days later, management arrived to close the facility. It was empty, stripped clean of everything. Not a lick of work was done in the 90 days, and nobody was there. There were reports that trucks had come to the loading dock, and took everything they could carry.

The cost of that led to the collapse of the company.