At this stage the cost is probably more in licensing fees and production costs than data streaming though.

But they play those previews automatically... and that's still bandwidth used.

And tragically most users prefer the auto playing previews. Theprimeagean has a YouTube video about how he tried to a/b test it before release thinking "no way that's what users would prefer" and was unfortunately wrong.

Well, there is a setting to turn it off.

My problem with turning it of is that if you _do_ want to watch the preview it's very cumbersome. Clicking on it goes to the movie/episode. So to get to the preview you have to go to the list of Episodes, scroll down (and try not to get spoiled) to trailers then play it. So I have one profile with it on and one with it off, depending on if I'm browsing or not.

Who's that and do they work for Netflix?

Tbh I don't mind the previews as long as they don't make the UI lag*. I was just pointing out that they don't save bandwidth.

* I'm also aware that they're blatant lies and have little connection with what's in the actual movie.

100%. Wasn’t trying to contradict your statement - just giving some additional context.

And he is a semi popular tech YouTuber that has risen to popularity in the last couple of years. I think he also streams on twitch but I’m not on that site so I can’t say. But he worked for Netflix for about 10 years.

A short, compressed, small video that's edge-cached beats always out a 4K stream, so it even works as a tactic to keep you in that overview longer.