The high and low points used in the high-low method tend to be unusual and therefore the cost formula for the mixed cost may not accurately represent all of the data.

The high and low points used in the high-low method may not be representative of all the data points, as they could be outliers or affected by other factors. As a result, the cost formula derived from the high-low method may not accurately represent all of the data points and may lead to errors in cost estimation.