Unless it's a form of foundation piecing, I'll bet they still use paper (or freezer paper). You're just not sewing directly through the paper, so there's not the hassle of removing paper.
It works great from some patterns, but is impractical for others.
And if it's on a foundation, that really limits you to the patterns you'd be able to PP efficiently.
Judy Mathieson, of Mariner Compass fame, used the freezer paper method in her most recent (?) MC book. It works very well.