As Hillcountry mentioned skid shoes too low will keep the plow blade up off the surface. If the plow person does many driveways some are probably gravel. In those cases skid shoes are almost mandatory early on when the ground is not hard frozen. Otherwise gravel as well as snow will get plowed. Putting the skid shoes back up for each paved driveway would mean getting out and manually adjusting the shoes. Not likely to happen.
When I had a gravel driveway and plowed it myself, the first several times each year an inch of so of snow was left which packed down to a hard icy surface. Once that happened I would raise the skid shoes unless a thaw came. If I had plowed many driveways I would have left the shoes down a bit all winter so that the plow was up a bit. That would also help avoiding plowing up lawns as snow is pushed to the side.
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