Dear GOD those things are annoying. They suck up time after every level and are completely useless on the boss levels while being a time vampire.
They are so blatantly just factored into the algorithm it is almost painful. Seriously even people who know nothing about the algorithm would raise an eyebrow at how completely worthless they are.
The first time you get one of the "You shall not pass" versions of the "boss level" it becomes so comically obvious.
I detest the things as much as Jelly Jars… and I HATE Jelly Jars and feel they are by far the worst blocker King has ever designed.