It is a big part of the communication, regulation and sensory system of cells. A lot of receptors are linked to ion channels for example. That's also the reason why there are pumps to bring the ions back on the other side too.
All these functions have appeared much later, most of them only in multicellular living beings, billions of years after the appearance of the living cells, and they have just adapted the already existing ionic pumps to other purposes.
In the beginning, ionic pumps had only 2 purposes, both essential for the survival of any cell, the first was expelling the ions that can form precipitates and the intake of the useful ions that are not dangerous, and the second was the energy interconversion between ionic gradients and forms of chemical energy like ATP hydrolysis/condensation.
