You can only afterEach on a non pollable queue. You can only check the queue size or poll a pollable queue. That said, I do not know why the two could not have been merged.
The documentation also says that:
"Unlike all other handle objects, PollableDataQueue instances do remain connected when they are sent to workers."
The practical implications of that do not come to mind.
Note by the way that the documentation on the two varieties of queue both say that the values are serialized and sent and deserialized, which answers points from your other question.