There are a lot of samples (food, environmental for US, environmental for EU, drugs of abuse, forensic, or any other type) to analyze.  That means there are a lot of samples to extract and run on the Gas Chromatograph.  We would like to spend as little time as possible on the sample preparation.  However, without sample cleanup the potential to contaminate the GC column and potentially the mass spectrometer source, if that is the detector.  The time that is saved in sample prep could be wasted in maintenance.  That is where backflush comes in.  Backflush on the PTV injector provides the means to remove the high boiling point contamination that will contaminate the column, and the rest of the system, that is missed during a fast sample preparation.