A switch input is one of the simplest interfaces to an MCU. However, when very low power designs are needed the pullup or pulldown resistor for the switch can draw a significant current. If the switch input is a momentary switch the current flow is very short so it is rarely significant. However, if the switch input is a door switch or level sensing switch
or any other switch which may remain in the active state for a relatively long time the energy used must be considered
Most of the discussion that follows gives examples for pull-up devices with the switches, the same principles apply for pull-down components. Also all the discussions assume that the EVdd = Vdd (all ports powered from the same supply voltage).
For more detail: Minimizing power consumption when sensing switch inputs
