DNA only replicates once in either mitosis or meiosis. I guess you mean how many times a pair of sister chromatids are separated. Still, once for either of them. The only difference between mitosis and meiosis is that mitosis forms 2 identical daughter cells with diploid number of chromosomes in a single 'split'.
Cell specialization is essential to an organism because cell specialization is what allows cells to provide the essential functions of life for an organism that have a wide variety of functions and purposes. Cell specialization leads to the diversity of cells in an organism such as the human body that build and allow essential organs and bodily functions to occur. Cell specialization is an essential building block that allows multi-celled and complex organisms to move and function.
