I recently came across an article called, "3 Bad Research Techniques That Will Ruin Your Work." The author, Dana Grinshpan, rips on the sampling method of snowballing. Snowball sampling is a research method in which you identify a group you wish to study, and then ask members of the group to identify acquaintances to also join the study.
Grinshpan demonstrates snowball sampling with Sudhir Venkatesh's study of gang life in the south side of Chicago. Veankatesh immersed himself in the gang and started by talking to a few crack dealers and prostitutes. They in turn referred him to other in the gang, and the sample "snowballed" from there. The downside to snowball sampling is that the group is no longer random, and no longer represents the population at large. Without random sampling, the researcher cannot make valid generalizations about the population at large, thus diminishing the value of the study.
Grinshpan then dives into snowball research, which is using the same process to find sources for a report. By reading one article, you can look at the author's sources and use them to find more and more sources. Again, this narrows your field of view and gives the researcher a limited perception with gaps in their argument.
A confirmation bias, a.k.a a snowball-point-of-view, is the tendency to test their hypothesis with positive examples rather than negative ones. People find sources that confirm their argument rather than ones that challenge it.
Snowballing can be effective if you are reaching out for a defined and very hard to reach audience (such as the Chicago mafia or gangs). Otherwise, the method should not be used. Snowballing creates biases, removes random sampling, and lowers the validity of a study.