Being fired for poor performance is all about ample warnings, issuing a PIP, etc. The company wants the employee back on track. Being laid off is a situation that an employee cannot fix with their efforts. There's no incentive to work this week if it is already known that you are going to be laid off next week, but some employees might consider a prank or even minor sabotage as a helpless act of protest. It's safest to dismiss the laid-off ASAP.