I agree no bushing is generally needed. I do frequently find Sheffield razors in horn with thrust washers. I just finished a Wosti today that had them and I reinstalled them. It was a pre-1890 razor. I do not find them on the early razors but I'll take a WAG and say they are common enough in 1870 and later blades. I think they make the blade pivoting smoother and keeps the scales from rubbing on the tang when closed. I install them as routine unless someone specifies not too. I think like in manufacturing today companies are always trying to lean out their processes. If they had not served a positive function the makers would have simply left them out and saved a penny a razor.