If you can make sure your template is completely degraded, the additional purification is not necessary. But utilization of PCR product without ligation step will reduce the efficiency of transformation.

Dear Lester Wu

if you refer to transformation in e.coli of a plasmid amplified by PCR (eg mutagenesis) supplemented with dpni to remove the background of template plasmid, you can directly transform it, dpni and its buffer do not interfere with transformation efficiency. If you are using genomic DNA as template for the PCR, the digestion with dpni is not necessary, since the genomic DNA, differently to the plasmid will not be able to enter and propagate into the E.coli cells.