One clear advantage of the qualitative approach to research is its ability to get information directly from the source. Qualitative research methods such as interviews and focus groups allow researchers to understand the thought processes of the subjects. This allows them to incorporate the subjects' subjective analyses of the situations into the research analysis. Such cognitive processes are untappable by quantitative methods.
Affect, or emotion, is an important influence of behavior. Social and behavioral scientists are often interested in the emotional state of research subjects. One advantage of qualitative methods is that they can investigate an individual's mood and emotional state, which allows them to understand behavior within that context. Without acknowledging the emotional state of the subject, researchers may be erring in making conclusions about the reasons for her actions.
One advantage of the quantitative approach to sociological research is that it's unaffected by the researcher's own subjective interpretation. Quantitative research methods are numerical, and so they can't be misinterpreted. This allows researchers investigating the same social phenomena to approach the investigation with the same quantitative method and compare results. If the results converge across studies, it becomes little less than a fact. This is something that doesn't hold true with qualitative studies, because all results are open to interpretation.
The ever-evolving fields of statistics and applied statistics give researchers using the quantitative method a vast selection of methods with which to analyze results. These forms of statistical data analysis allow researchers to know a large amount of important characteristics of the data, including variables' relationships to one another, differences between groups and even the likelihood that the study yielded incorrect or inconclusive results. This is in direct contrast to qualitative studies, which can always be interpreted to have important results.