If you are cleared for FL320 and you turn the rotary selector just 1 click too far you would have entered FL330 iso FL320 when 1,000ft increments are selected. During phases of high workload, such an error could remain undetected.
With 100ft increments, the selected level would be FL321, which does not look right at all. Therefore, the 100 ft setting increases your chances to notice some fingertrouble.
Of course we are talking of propablities of 10E-x.