Surface area: Volume Ration is a critical factor for cells. Small cells have a high surface area:volume ratio and hence efficient at transport at and diffusion of molecules across their membrane. Alternatively, large cells have a low ratio and are less efficient at diffusion.
A good example of a cell with particularly good design is human red blood cells. They have no nucleus, to reduce the volume needed, and have a bi-concave shape to increase their surface area, allowing faster exchange of Oxygen and Carbon dioxide.
There is a possibility that DNA may only be able to exert influence over a finite volume, and this creates a limit of cell size. SA:V ratio also limits further cell growth.
