Polyclonals can be used for Western blot, immunohistochemistry on frozen slices or parrafin fixed tissues. The advantage is that there are more epitopes available in a polyclonal antiserum to detect the proteins than in monoclonal sera.
If you buy Antibodies supplied by allele they should be stored frozen at - 24°C for long term storage and for short term at + 5°C.
Polyclonals and antibodies
Genetic Disease Markers