These checks are designed to ensure the voltage of the electricity is strong enough to ensure that the binary high value never dips below a specific margin, due to the millions of transistors that are switching.
In the design of a printed circuit board, the power supply is uniformly distributed across the board. The metal layers in the board have a finite amount of resistance. When the board’s voltage is applied, some voltage will drop due to the resistance. This drop in voltage is known as the IR drop.