An occupation at a central urban location could serve at least three purposes:
1) Providing safety, community, and other basic aspects of a decent existence, for those who currently lack them.
2) Creating a hub for socializing, coordinating projects, etc. - for any activity that can benefit from the availability of a 24-hour, centrally located meeting place.
3) Spurring progress toward more optimal organizational methods in society at large. Organizational methods centered around violence and domination still hold sway around the world, to different degrees in different places. We can participate in the important and fascinating project of cultural evolution by creating spaces where voluntary, cooperative organizational methods are practiced, refined, and demonstrated.