On United I can check bags up to 75lb (34kg) for free due to status, regardless of fare. I can't remember the last time my bag was weighed or marked.

Indeed, now that I look, some airlines allow higher per-luggage limits. I wonder if it's new, and it's due to more automation of the handling.

Anecdotally, I flew Norwegian recently and I was the only one that handled the luggage. I had to figure out how to attach the label, which was mildly intimidating.

I believe there is a very high fee attached to checking in 23kg-32kg bags (€80?) which are then specifically marked. It wouldn’t surprise me if it’s added for free on some business class fares.

Higher limits usually mean several bags.