Answer: Efficient functioning.
Explanation:
Cells require a lot of substances to both come into and leave the cell in order for the cell to accomplish it's functions. These substances can be anything from carbohydrates to water and they come into the cell through diffusion and osmosis.
The thing about diffusion however, is that it happens faster over shorter distances than longer distances. This is why cells are so small. They evolved to be that size to ensure that diffusion of these substances takes place relatively quickly so that they can use these substances to carry out their functions at a faster rate.
