There are some guidlines to know so you can gage when rehabs are necessary.
1. If a person is abusing drugs or alcohol and gets to the point where they recognize this is causing them problems and they make an honest attempt to stop using on thier own but cannot.
2. If they are absuing drugs or alcohol and manage to dryout on thier own and start attending 12 step meetings and the telling of thier drug and alcohol relatee stories in these meetings ends up triggering relapse.
3. If you have been through one rehab program and have some amount of clean time and them relapse you should look for another rehab.