One approach includes both reward / consequence. In this model, things like theft, various forms of violence particularly in shelter or public housing violence, even taking over extremely large areas of public space (ie, 3-4 tents plus dogs plus...) results in consequences, while avoiding issues along the above lines results in rewards (ie, eligibility for service or additional service). In addition, these approaches tend to also consider impact on the non-homeless (ie, prison time linked arguably with a reduced risk of property crime)
Other models are focused primarily on making life as bearable as possible for the homeless - basically the straight service model. Under this model, resources are provided and consequences are reduced in the event to solve homelessness.
Some folks going through the tougher love systems (ie, jail vs rehab etc) say good things, other folks ask how can homelessness be criminalized and focus primarily on reducing risk of govt involvement (this can also save money in some cases - prison is expensive, rehab is expensive etc).