MgCl2 is an essential cofactor that boosts the performance of Taq DNA polymerase in PCR, thereby increasing the rate of DNA amplification.  It also enhances the amplification efficiency of the reaction. 

MgCl2 also boosts PCR efficiency by increasing the melting temperature of the reaction. The melting temperature refers to the temperature required to half denature a DNA template. 

Another significant way that MgCl2 enhances DNA activity in PCR is by facilitating effective and accurate template primer binding. This is due to the Mg2+ ions binding to the negatively charged alpha-phosphate of a dNTP and removing the remaining two phosphates, thereby decreasing the electrostatic repulsion between DNA strands. This prevents renaturation of the DNA and stabilizes the single-stranded template DNA.