The farrier/horseshoer usually bends a bit of the metal at the toe or along the sides of the shoe to create the clips. The clips, as far as my experience has been usually help take the pressure off the nails and keep the shoe secure; also a toe clip might be used in conjunction with "rolling the toes" to cause the horse to pick up the foot a little earlier than they might otherwise be inclinde to do; horses that clip (catch the back of the front foot with the rear toe) often have clips and rolled toes and squared toes...corrective work to try to keep them from pulling off those front shoes....