This is from the King Arthur flour site and it is for scones but the same techniques are used for mixing biscuits. I do this when I make scones and I would bet it would do the same for Baking Powder Biscuits.
"Why freeze the scones before baking? Because 30 minutes in the freezer relaxes the gluten in the flour, which makes the scones more tender and allows them to rise higher. It also chills the fat, which will make the scones a bit flakier."