Deadband (and hysteresis)

Without a deadband, an on/off system such as a thermostat would switch every time the temperature wobbled by a fraction of a degree. A hysteresis band (turn heat on a little below the setpoint and off a little above it) trades a small amount of accuracy for far fewer cycles. Compressors, relays, valves and pumps last longer and usually run more efficiently when they are not short-cycled.

Hysteresis also shows up as an unwanted property of mechanisms and sensors: gear backlash, valve stiction and some sensing materials respond differently depending on direction. That kind of deadband is a problem to manage rather than a feature, because it makes fine positioning loops hunt back and forth.

A practical rule: the band should be wider than sensor noise plus expected overshoot, and narrow enough that users don't notice the swing. Equipment makers often specify minimum on and off times; the control logic should enforce them.