Descaling is the cleaning process that removes the buildup of calcium and limescale. The latter is a hard, off-white, chalky deposit found in your coffee maker that can affect its drip operation.
Calcium and limescale are not toxic but their buildup can affect the quality of your brew. Water in the reservoir may not reach the optimal brewing brew due to limescale buildup insulating it from the heat source.
As a result, the full flavor of the coffee beans will not be extracted. Also, your coffee may not be as hot as you would like it to be.
Limescale buildup can also disrupt the drip operation of your coffee maker. It can cause it to work harder and ultimately, its breakdown.