Don't get attached to your early access worlds--nature of development, there will be times where you need to restart for new content to work. If you're really attached to one then world hopping is your best option. As for the usefulness of tar--right now it's got some crafting uses but I wouldn't be surprised if it became useful for more things as Early Access provides more content. It's a resource--maybe not vital immediately or even ever for that matter, but it's another option in the game if you want to pursue it. Don't like it then don't use it, completely your choice.