Here a short video about the Island One space habitat:
Free space habitats like Island One are an alternative for, instance, the colonization of Mars. A major advantage of this kind of space settlements, is that they can be located anywhere,
We could decide to start space colonization close to Earth, using the Earth-Moon Lagrange points. This would mean that travel between Earth and Settlements could be done within a week, rather the eight months a trip to Mars would take. In case of an emergency people could be evacuated to Earth quickly, which is not possible with Martian settlements.
Free space habitats provide a more gradual approach to colonizing space. Once our experience with space settlements in a near earth space, we could consider to build space habitats at the Sun-Earth Lagrange points or in the Asteroid belt.
In the lung run space habitats are a better way of preparing mankind for interstellar travel than Martian or even Lunar settlements could. A space settlement is essentially a generation ship.