What is the use of an antibody that is non-neutralizing?
The term "neutralizing" depends on context. In virology, it generally (not always) means it prevents the virus from binding to its receptor(s) and getting its genetic material inside the now-infected cell. Other antibodies can bind other epitopes besides the sites of binding between capsid and receptor (or enveloping membrane and receptor), yet still contribute to the immune response. Such antibodies are often opsonizing. Still more antibodies are just ineffective, a byproduct of the antibody maturation process.