This happens in all cells in the body. It occurs when you want identical copies of a cell. It happens when the chromosones in a cell form along the equator of a cell and are split apart, they are then drawn to seperate poles of the cell. They are now chromosones in their own right! The cell then divides creating two cells that are IDENTICAL!!
This happens in the sex cells (gametes) when you want to make daughter cells. This is when 46 chomosones (23 from the spem and 23 from the egg) come together and are split in the same way as Mitosis. This then creates daughter cells that are similar to the parent cells but are NOT the same!