Positivism matters in that it impacts our ability to trust our own observations and the conclusions and resolutions drawn from our observations. If we are able to examine in a positive light, i.e, truly perceive what truly is, then our results are trustworthy. If we are not able to truly see past our own culture and social psychoses, as historian Page Smith called our social "blind" spots (where we do not perceive our own actions and motives truthfully), then it is not possible to trust the results of our examinations of others.
I think positivism is important because without it we would have to conclude that any sense of objectivity is impossible to achieve as we look at the world around us. Positivism is therefore valuable because it allows us to make conclusions on what we are able to objectively see, whilst also indicating the way in which objective knowledge is often difficult to attain.
For social scientists, positivism is a philosophy which has to do with the ways in which observers perceive the subjects that they are studying. Positivism holds that observers can look at their subjects and see true facts about them. Positivism is opposed by epistemologies that argue that we are unable to look objectively at other people or cultures. These philosophies deny that there can be any objectively true facts when it comes to the social sciences. All of what we perceive as facts are simply our subjective opinions about what we observe in our subjects.
The term matters, then, because we have to think about whether positivism is a valid philosophy whenever we try to study other people or other cultures.