Jellyfin/Plex/Emby turn your media collection into your own personal Netflix. They have apps for multiple platforms, you can setup user access controls, parental controls based off age ratings, track progress through shows and movies, search and organize based off genre and tags, and much more. Also, they can handle on the fly transcoding of the media, so if a device doesn't support a specific codec or container it can be converted into another, or if the user is on a poor Internet connection which can't handle a 4K video, it can downgrade the quality to make it easier to stream on the poor connection.

Overall, they just provide a better experience when consuming media.