Indeed. I never understood the point of it. It made sense in Inbox because Inbox would only show you the Promotions bundle once per day (or at your preferred frequency) but after they shoved the feature into Gmail it stopped making any sense.
I think it makes sens for people who get themselves signed up for all kinds of newsletters they don't really want and then can't find anything in their inbox. So really it's just another anti-spam filter and comes with the same downsides.
Yes, I've always been baffled by this. I like the idea of it, but when you actually use it and think about it, it actually makes the experience worse.