Why might polyclonal antibodies give better results than monoclonal antibodies?

Although monoclonal antibodies tend to have lower cross-reactivity and produce lower background than polyclonal antibodies, polyclonal antibodies can give higher signal and better results than monoclonal antibodies, especially if the protein of interest is in low quantity. The higher overall affinity and sensitivity of polyclonal antibodies is the result of binding to multiple epitopes instead of just one. Monoclonal antibodies may also not be as effective in the case of polymorphic antigens since those antigens possess variants.