Without it or when it is diminished, performance in every area of life suffers, including flight and maintenance operations on all sizes of aircraft on any field in the world. Fatigue resulting from sleep loss may be the result of a sleep debt built up over time or acute sleep loss. Any college student who works and goes to school full time may grab 5 to 6 hours of sleep each working day, but on his day off, sleeps in to try to satisfy this debt. An aviation maintenance technician who works a couple of long shifts will also sleep off his debt on his day off. This is a normal, necessary process.
Rest is important.
The human body sleeps best in rhythm with its temperature highs and lows. Beyond the burning eyes, microsleeps or momentary zoning out, and hiccups in short term memory, perhaps the most insidious effect of fatigue is what it does to motivation in both pilots and aviation technicians. Otherwise experienced pilots who become overly tired can exercise poor judgment as a result of their rush to accomplish a flight so they can rest. They may perform an inadequate preflight, or fail to complete all checklist items in preparation for an approach. Aviation technicians may rush to get the last plane ready for takeoff.