A cell must maintain its ATP current – this means that wherever ATP is used, it must be replaced. The distribution of ATP is every bit as important as the concentration, and there can be problems with either or both.
For example, for the ion pumps in the cell membrane, ATP -> ADP + P; neighboring ATP replaces the hydrolyzed ATP, and this new ATP came from where it was generated, while ADP and Pi travel to the mitochondrion and enter through specific transporters. During mitochondrial respiration, ADP is phosphorylated in complex V, as proton motive force is used to drive the phosphorylation. ATP translocates back out of the mitochondrion to replace the ATP that was used by the ion pumps.
To maintain viability, the cell must maintain its ATP current. Too much of a decline in the flow of the charged molecule, ATP – which requires transport, regeneration, and transport back – would compromise the cell’s survival rather quickly.