I think that having open exploration dungeons adds an element of getting to know your server community. On small servers like Mateus (the one I'm currently on), it's incredibly hard for people to be social and to party up or make friends. The Duty Finder is great for people who can't find members, but I think open exploration dungeons adds a new way to meet and team up with folks that are on your server. The downside of Duty Finder is that you can't party up again with the same people because it takes players from different servers.