S-phase is the part of cell cycle. In this phase, DNA is replicated between G1 and G2 phase. Accurate DNA replication is needed to prevent genetic abnormalities. The abnormalities lead to cell death or mutations, which cause conditions like cancer or instability. So, regulatory pathway is highly conserved.
By preventing the S-phase, the system would work, but certain DNA repair mechanisms like post replication recombination repair would not happen prior to cell division. The 3Rs are important for proliferation, evolution, and maintenance of genomes.
Also, without replication, there would be just two cells instead of four cells as a result of meiosis.