Or at least, it's bad for the gene expression in the immune systems of female rhesus monkeys.
Social environment can have effects on your health. People (and animals) in bad social conditions are more susceptible to illness, and bad social situations can lead long term to issues like fertility or even survival. We’ve known about the correlation between social stress and health for a while, but most of what has been studied in humans about social environment and health has been correlational. You can’t really determine whether the social environment alone creates the problems. But if you have an animal model, it’s a lot easier to manipulate social environment, and to then look directly at the effects of social environment on various health measures.
Using an animal model allows you not only to separate out social environment from other variables, it also allows you to look at mechanism, and try to see what changes in what areas produce the global susceptibility to illness and other problems associated with social stress.