In the last few years, there have been several proposals to use lots throughout the city of San Francisco that are slated for development as interim green spaces. The idea behind this is that using land for temporary parks or public spaces while development is stalled (happening frequently in this economy) is better for the community than having a chain link fence marking off the boundaries of a lot.
It's all about balance. And about designing legislation that meets your desired goal. Or perhaps that is exactly what is happening here.
Those living in San Francisco benefit from lower transportation costs, and in many cases, lower housing costs.