For Cast Iron pans, do the grill pans make a difference?

They drain the fat away from your food, not just cosmetic to give it lines! Stupid people, telling you rubbish!

The ridges in grill pans serve several purposes. First, as you know, they give your meat a nice pattern of grill marks. Second, as someone else indicated, they keep your meat elevated above the fat that drips out of it, so the meat is not frying in its own grease.

Third, the grill pan ridges take advantage of three different methods of heat transfer:

A) CONDUCTION - heat is transferred by direct contact between the metal and the meat along the tops of the ridges, just like a normal skillet.

B) RADIATION - heat is radiated from the bottom of the troughs between the ridges, the same as it would under a broiler or in a real grill.

C) CONVECTION - fat drips down into the troughs between the ridges, hits the superheated cast iron and turns into smoke, which then drifts back up toward the meat carrying the smoky flavor of the burned fat, just like a regular grill. It is this smoke that gives barbecued meat its distinctive smoky flavor.

Thus, as you can deduce, with all this heat transfer going on and the smoky goodness enveloping your meat with its delectable aroma, grill pans are more efficient than skillets, and produce a better flavor in your meat in a shorter time.

Certainly the results of using a grill pan are NOT just cosmetic.

Cosmetic. Rarely use that side of the grill pan. Use the flat side. One with a oil trough on it. Unless you are fixing for company were you wish meat with the marks on it. Buy one big enough to cover 2 burners. Better heat control. Searing side and cooking side. Then once seared turn heat down there to warm side. That is a flat grill.

they are cosmetic