When I was in high school, I had a classmate who was having a lot of trouble. She legally emancipated herself at age 16 because her family wasn't supportive of her at all. She was living with her grandmother and paying rent. However, as a high school student, she couldn't make much money. She was choosing between rent and food pretty often. During senior year, her grandmother was going back to their country of origin for 6 months and wasn't able to keep the apartment. My friend was thinking about dropping out of school so she didn't have to move back in with her mom or dad.
My mom and I talked about it and decided to invite her to live with us. My brother had moved out a few months earlier and we had an extra bedroom. My friend is not the kind of person to accept help and was hesitant to move in. She began staying with us a few days a week and eventually moved in. She lived with us for about a year and we got her off to college.
It wasn't the easiest situation (there were issues with her now-ex), and she didn't follow through with everything she said she would do (cleaning, cooking). However, neither my mom or I will ever regret taking her in. She's brilliant and doing great in college. She would have been a high school drop out had we not helped her.
Obviously, this was a different situation than many others that have been discussed here. But my point is that while these situations can go badly, the benefits to you and others can outweigh the negatives.