You can't "easily" manipulate it year after year. It's a myth.
It's like your domestic finances. You can borrow a bit here and save a bit there to get by. And if you stop there you can be ok. You never get even, but you can manage the debt. This is the Steve Keim way.
But when you start borrowing from one bank to pay the interest on another loan, then your into the loan sharks to pay off the banks it eventually comes crashing down. You can look flush for a while while the debt is piling up, but before long you're living in a cardboard box.
And that's where the Saints are going into next year and it's where the Rams are heading.
There's no magic trick. There is a set cap each year (consider it income) and if you're borrowing now from future income the time comes when you have to tighten your belt and live on baked beans.