The major advantage of such schools is that they prepare students for real life. In real life (at least in the West), men and women must get along together. They have to be able to work together regardless of the fact that they are of different sexes. Coeducational schools give students practice doing this.
The major disadvantage is that the students might be more distracted than they would be in a single-sex school. Boys, for example, might want to act macho so as to impress girls rather than paying attention in class. Girls might not want to talk in class so as to avoid looking "too smart," which might make the boys less interested in them. This might mean that both boys and girls would get less educational value in a coeducational school.