In the last decade or so, I've seen more and more lens hoods for long lenses that aren't simply round in front. I was reminded of that by this answer, which shows the inside of a neatly packed camera bag. In particularly, here is the telephoto lens from that picture:
In this case, it looks like the lens hood can be detached and flipped backwards on the lens for easier storage.
I thought the point of a lens hood, particular for a long focal length lens, is to shade the lens from angles it's not going to make a picture of anyway. This is useful, for example, for keeping the sun off the front of the lens when you're not trying to include it in the picture. This prevents internal reflections from bouncing around and getting into the picture, even though the sun or other bright light is not actually in the picture.
A round lens hood, like on my old 300 mm lens makes sense for that. So what's the advantage of this tulip-shaped lens hood? Either you want the hood to shade the lens or you don't. As long as it doesn't get in the way of the picture, more is better, right? Presumably the peaks of the tulip don't get in the way of the picture, so how can the cuts in between the peaks be helping?
What am I missing?