For riders with a wider stance width the pedal spacer will improve the foot/knee/hip alignment.
The aluminium pedal spacer helps riders with knees that track outside of the pedal.
1.5 mm pedal spacer washers are used with knees that track outside the pedal by adding length to the pedal axle. They're designed to move the foot out and away from the crank arm to provide more foot clearance by adding to stance width for cyclists needing help with knees-out, excessive toes-out, extra wide feet, wide hips, or for those with discomfort on the outside of the knee.
Note: 1 is the maximum number of 1.5 mm Pedal Spacer Washers that should be used on one pedal unless you are using Look Pedals, or you are a professional bike fitter.