I liked features like director commentary and deleted scenes (usually deleted for good reason but still interesting)
Boy oh boy did that LotR premium extended something-something edition on DVD turn out to be a godsend with the countless hours of behind the scenes footage and interviews, and director's commentary. I watched it all.
That blew my mind and was an awesome experience. In the age of dial-up internet it wasn't like you could find and / or watch that online.
doom9 had reams of guides dedicate to the matter: https://forum.doom9.org/showthread.php?p=313722
In the peak of the DVD era my SO and I were both big movie fans, and at one point had watched literally everything the Blockbuster and Hollywood video in our neighborhood had. There just wasn't the embarrassment of riches of the post youtube world.