Any increase in the number of homes reduces the homeless population. There are so many homeless people in CA mostly because there just aren't enough homes for everyone there. It won't completely solve homelessness - many people living on the streets now need social services and therapeutic help before they can afford any rent again, but there's plenty of homeless people in California with fulltime jobs paying like $30k/year (around the median salary in France). If you build enough homes, these people would be able to find housing, and social services would be less strained for the people who really do need help.