you need a bit of fat in any burger to make it moist or else it will be as dry as a terracotta roof tile baking in the arizona sun
the skin contains fat
so your dad's making a moist burger
always better to grind your own if you can
that way you add the seasonings right there without having to get too messy
There are some great commercially formed turkey patties without 'cutters grade' shite in them: Shady Brook Farms, Louis Rich, even the Hitler of Poultry, Mr. Frank Perdue, has a decent product. I like the shady brook ones. chomp.