High idle is when the engine runs at higher than normal RPMs, usually over 1,000 RPMs. Although high idle can be beneficial in certain situations, such as warming up your car on a cold morning or running heavy loads with an automatic transmission, it can also cause damage to a vehicle if left unchecked. The potential damage that high idling can cause includes excessive wear and tear on the engine components such as spark plugs and pistons; increased fuel consumption; decreased performance due to inefficient burning of fuel; and reduced life expectancy of the engine components. High idle can also lead to overheating problems since more fuel is being used while at an elevated RPM level which leads to increased generation of heat within the motor. This could result in long-term issues such as cylinder head warping or even cracking which would require immediate repair or replacement resulting in costly repairs for any vehicle owner. Ultimately, it's best practice to keep your car's idle setting at factory defaults unless there are specific reasons why you need a higher setting - otherwise you risk doing unnecessary damage to your vehicle leading to premature failure down the line.