I tend to agree about the waste of space, but using it on the desktop it's good for discoverability by lazy scrolling, I think.

At least I discovered many articles that way, lazily switching categories, which I'd have missed otherwise.

There are other HN-frontends which do similar things, but with the exception of [1] https://hckrnews.com/ none stuck with me so far.

This one I liked, bookmarked, and intend to use more often until further notice.

edit: What is missing for me is the ability of simple "click-through" to the original HN for voting/commenting without having to give my user/password to another site. That won't happen!