But my point is that if there is a relation of trust between the PM and the developers, padding is unnecessary.

I had PMs to who I could give optimistic estimations and risks. That way, the PM could plan the different scenarios (like extra features in case we had spare time).

Other PMs, the ones who converted estimations into deadlines, got lots of padding. And the problem of adding padding is that it is time lost, because a developer who adds padding cannot tell that they finished earlier.