If a cell did not make a second copy of all its DNA before cell division, it could result in a variety of issues such as mutations, chromosomal abnormalities, and genetic disorders. This is because each daughter cell would only receive a partial set of genetic information, leading to incomplete or faulty genetic instructions. This could potentially cause the cell to malfunction, fail to carry out its normal functions, or even lead to uncontrolled cell growth and cancer. Therefore, it is crucial for a cell to replicate its DNA accurately and completely before dividing into daughter cells.