By having an organism’s entire DNA data included in each cell allows for a type of fail safe system. If anything should ever happen to that cell the DNA data is not lost as would happen if it were only assigned to a single cell. This process also allows cells to be independent of each other. They can reproduce as needed to replace dead or damaged cells and they can stop the reproduction to prevent an over abundance of the same type of cell. (in a normally functioning cell)
If we only had one source or a central repository for our DNA any loss or damage to that source or repository would result in our body not being able to repair what it is capable of and our system would cease to function which would cause the end of our existence. Again, I look at are system of each cell containing our DNA as a redundant fail safe method.
By there only being four different bases in DNA strands we still have the vast diversity in nature due to the almost endless possibilities of combinations of traits which can develop from the paring of these bases. With the recombination of all of the genetic material in an organism’s genes you have the potential for a huge variation of expressions of that material.
By having an organism’s entire DNA data included in each cell allows for a type of fail safe system. I