Electric companies use sags to cope with extraordinary power demands. Hot Summer days, when air conditioning requirements are at their peak, will often prompt rolling brownouts.
Sags also reduce the efficiency and life span of electrical equipment, particularly motors.
Akin to the force of a tidal wave, a spike can enter electronic equipment through AC, network, serial or phone lines and damage or completely destroy components. Spikes can also occur when utility power comes back on line after having been knocked out in a storm or as the result of a car accident. Data will be lost. When this equipment is switched off, the extra voltage is dissipated through the power line. It may be intermittent or chronic.