Why do we do nested PCR?
In the paper by K. Lily Therese, U. Jayanthi &amp; H.N. Madhavan traditional PCR wasn't sensitive enough to allow for an accurate reading on what they were trying to study. By using nPCR they were able to amplify around the gene they were interested in and then amplify just the gene they were interested in for a more accurate and sensitive study. The successive PCR allowed them to amplify their specific gene even if there was only one copy in the sample. 

I recall using this procedure in Molecular Genetics Lab, it was used to make sure that our sample was purer.