[NedSVS]

They (the washers) are there to protect the frame lugs. Even if the spacer was the correct length without them, the bearing spacer would create a depression in the relatively soft aluminium frame lugs when the bolt was fully tightened and the lever/knuckle would be able to rub against the frame lugs - worn frame lugs can't easily be replaced but the washers can. I seem to remember someone on this forum accidentally leaving them out and cracking a frame lug when they tightened the bolt!