According to Bentley and Ziegler, St. Benedict and St. Scholastica were very important because they helped to create the monastic system. This system, as discussed in the answer to another of your questions, became very important in early medieval Europe. Because the monasteries were so important to the Europe of that period, the two siblings (they were brother and sister) were very important.
Before St. Benedict and St. Scholastica, there were communities of religious that could be called monasteries. However, these communities had very different expectations of their members and were not really connected to one another in any important ways. In response to this, Benedict wrote his Rule for monastic life and St. Scholastica adapted it for women living in convents. By doing so, they created more disciplined and organized monasteries.
When the monasteries became more organized, they became more important as a social and economic force in Europe. They were able to attract more members. They got bequests from wealthy individuals that allowed them to become more important. Their numbers and the amount of land they had allowed them to be a major economic force and to help expand agriculture in various areas of the countryside. As this happened, they became more important to European society in the ways mentioned in the link above.
Thus, St. Benedict and St. Scholastica are important because they helped to create the monastic system that was so important to early medieval Europe.