It plays commercials during act-breaks or something, like a network broadcast. I haven't used it though.

I'm enough of a Trek fanatic that I've had CBS All Access from the start, even between seasons. But I've never watched anything other than Discovery and the three or four disappointing episodes of Twilight Zone that I got through. Occasionally I go there to catch a Colbert interview or something. Even the old Star Trek shows I still watch on Netflix, maybe just out of habit.

I'd definitely watch old Lettermans if they posted them, but I'm probably one of very few. More importantly, Dave's CBS deal was so good that I think now he actually owns the episodes. So they'd have to cut a deal for that.