When you have a layoff, the former employee can file for unemployment. Which is money that comes from the company (through a circuitous route). So it's cheaper to go "mandatory unpaid leave".
So this is a scumbag move by the employer then? They don't want to lose the employee, they don't want to pay them, and they don't want to pay for unemployment?
Well, that depends. On the one hand, maybe it means that they are expecting to be able to survive long enough to bring everyone back and are wanting to cover insurance benefits a bit longer. Or perhaps it means that they are trying to use the current bank account balance (presumably a few months worth) to stay solvent a bit longer, hanging on to the point where they have absolutely no money left-- when of course everyone's unused PTO would disappear.
Staff are still on the books so that the business doesn't have to go through all the paperwork of firing (and possibly re-hiring when business resumes).
In addition to the cost of paperwork, there's also the issue of paying out unused PTO. In many cases like mine, this can add up to many thousands of dollars per employee.
What does this mean, precisely? How is it different from firing staff?