Here's why this is important:

* DNA polymerase's primary function is to synthesize new DNA strands. It does this by adding nucleotides to the 3' end of a growing strand.

* The 3' to 5' exonuclease activity is a proofreading mechanism. If the polymerase accidentally adds the wrong nucleotide, it can backtrack using this activity, remove the incorrect nucleotide, and then add the correct one.

* This proofreading function is crucial for maintaining the accuracy of DNA replication. Without it, mutations would occur much more frequently, leading to errors in protein synthesis and potentially disease.

Let me know if you'd like to know more about DNA polymerase!