This has always struck me as a weak justification. If readers value succinctness, the problem should solve itself without any need for restriction, because people would follow those who get to the point and unfollow those who don't.

If somebody chooses to be a windbag and someone else chooses to follow them, why should Twitter be standing in the middle telling them both that they're Doing It Wrong?

For what it's worth, I don't find it good for readers. People tend to leave out context and nuance.