PCR products contain amplified fragments and PCR reagents. Also, there might be a small amount of gDNA, which you had used for the first time. so, if you want to amplify the fragments ones more, I think the fragments, as well as the targeted portion of gDNA, would be amplified simultaneously. Sometimes. in case of gDNA, there might be some cases of mispriming.

So, I think purified PCR products would be a good practice in this regard.