Mitosis is the process by which genetic material found in the nucleus is replicated. This is usually performed in conjunction with cytokinesis, which is the division of the cell, cytoplasm, and all the associated organelles.
Without this process of genetic and cellular division, large multicellular organisms, such as humans, would not be possible. If cells did not have a mechanism by which one cell could grow into many other cells, then all organisms would have to be small, unicellular organisms like Amoeba and Paramecium. The process by which an egg cell is fertilized and divides into a multicellular organism would not happen. Also, if it were not for continual mitosis, then organisms would not be able to grow or replace damaged cells.
Though mitosis has been understood for many years, it is still a relevant subject of study today. Cloning is greatly dependent on mitosis. Basically, scientists are now able to coax mature cells to go through the same mitotic divisions as they usually occur in embryological development. Mitosis is studied in relation to cancer research, which looks for small mistakes in the mitotic process that can cause mutations and lead to cancerous cells.