It's definitely fun to creating the ultimate fantasy and sci-fi settings. In fantasy, you can have tons of non-human races, mythical creatures, elemental planes, gods, all kinds of magic, and many places of the world based on all sorts of historical cultures and periods. Magitek/Dungeonpunk would also be included. Of course, it would have influences from tons of fantasy authors, like Tolkien, Howard, Moorcock, Lieber, Vance, Fiest, Le Guin, Hickman & Weis, Salvatore, etc, as well as tons of mythologies, like Arthurian, Celtic, Norse, and much more.
In Sci-fi, it would take place in the far future. There are Thousands of different race, as well as planets. Each planet would have its own geography, as well as flora and fauna. Humans would be called 'Terrans' and the planets of their old solar system would be fully inhabited, incuding terrain planets like Mercury, Venus, and Mars, moons like the Moon, Phobos, Deimos, Europa, and Titan. The gas giants Jupiter, Saturn, Uranus, and Neptune would have lots of floating cities inside them. Even Pluto would be inhabited. Psionics are a mysterious power in the universe, faster than light travel is completely possible, spaceships range from small pods to space stations, and not only would ballistic weapons weapons exist, but others like gauss weapons, lasers, plasma weapons, and other types of energy weapons.