I've got a few worlds setup so far. They are named based off of what I plan to do in them.
1. Build World: This is where I build things in creative mode. I can go crazy with whatever blocks I want in order to make that new, amazing battleship BP.
2. Test World: This is where I test things. It could be spawning in ships for combat testing, or where I build some of my projects that have a high chance of backfiring or just generally exploding themselves, or the area around them. Examples include: Drone swarm battles, and Warhead testing.
3. Tutorial World: This is where I am working on videos I plan to upload to youtube. Mostly tutorials, and hence the name. (recently created world)
4. Survival World: This is where I just play the game. I actually just gave this world a fresh start after being out of survival for quite some time now.