Answer:
I'll assume this is crossing over-- as in meiosis.
If so, it's an enzyme-mediated process that takes place in the prophase of meiosis.
But, I'll just cut to the chase:
Crossing over is important because it creates gametes that can yield more genetically diverse offspring.
To be more exact, the genetic diversity is due to the exchange of genetic material between homologous chromosomes. This will give new gene combos on each chromosome.
I hope this helps!