PCR performs the amplification of a next-generation sequencing (NGS) library. In addition to increasing the amount of DNA, the PCR amplification step also enriches for fragments that have an adaptor-ligated to each end. These will be the fragments that attach to the flow cell and will be sequenced. It is important that this PCR step does not introduce mutations to the library, as a lower error rate means that less sequence coverage is required, saving expense and time.