A couple I can provide --
Family's home burned to the ground. Candidate spent entire senior year living in hotel room. Since parents didn't speak English, candidate spent much of the time interfacing with insurance companies, home repair companies, etc.
Candidate's father was a geographic bachelor and mom worked long hours. Candidate fixed breakfast for 3 siblings, drove them to school, picked them up, cooked their dinner and helped them with their homework.
The above said, not everyone has such an experience -- 4/5 of the incoming class did not. Most of the time, it helps explain lack of ECAs, sports, etc. -- not sure it per se is a huge bonus in the admissions process.