A functionalist might ask what schools do for a society beyond teaching a syllabus: they also bring people together, pass on norms and organise qualifications. This perspective looks for relationships among institutions, as one might examine how parts of an organism work together.
The question can be revealing, but it can also make an existing arrangement seem necessary merely because it has a role. A practice may benefit some people while harming others. Asking whose needs it serves keeps the analysis from turning description into approval.