This has been the standard for the 68 years I have been riding. Almost anyone with long time riding experience would tell you that. I would guess some of the reasons would be no W/S distortions, better dynamics, better wind flow i.e. carbon monoxide and others. And last but not least, lack of wind therapy.
I use the same method by lowering my W/S on my Spyder. Most ride with a full face Helmet with shield or at least a face shield as they should to protect eyes. Looking through the Face Shield and the W/S will normally give some distortion and a small percent of visibility loss. Of course this does not apply to the "Gold Wing" rider that rides with shorts, penny loafers, a t-shirt and no helmet. He needs the biggest W/S he can find!
Jack