In his book "What the Dog Saw" - "Million Dollar Murray" , Malcolm Gladwell explains the power-law theory of homelessness by Philip Mangano: http://gladwell.com/million-dollar-murray/.  Though not popular, economically it's wiser to target the chronically homeless with free housing than it is to spread the same amount of public resources around to more people in need.  That's because a small handful of people account for the vast majority of burden on public and health care services (thus the power-law theory).  An interesting read for people who think it unwise to help those who have fallen so low they cannot climb out by themselves.