mitosis is important for a lot of reasons. Cells divide in order to increase or have a higher chance in their surface area to volume ratio. As a cell grows this ratio becomes such, so that the cell can not take in nourishment and essential compounds quick enough not even gets rid itself of wastes since the volume is so many times more than the surface area available. To lower this ratio they divide or get smaller depends on how you want to think of it right. In organisms that are multicellular, cells reproduce by mitosis in order to grow in size, repair ruined or dead areas, take the place of the dead cells.
Really hoped this helped:)
