I have observed on cars with disk brakes, new and old cars, that sometimes the pads are in front of the axle and other times behind it. There seems to be no consistency. I can look at 2 similar SUVs, or any 2 similar cars, and they are the opposite of each other. This occurs on the front and rear wheels. It doesn't seem to be a space issue for there seems to be clearance on either side of the axles to do it either way on any car.

Is there any mechanical reason why or it is just complete aesthetics?

I was trying to figure out whether there was some mechanical advantage the manufacturer might be trying to take advantage of by the particular placement. For example I would think that if the pads on the front wheels are in front of the axle then push the axle down and thus create a little more tire grip. Or maybe there are 2 forces that are canceling each other out and the net effect is zero............and I am just too fried right now to think it through clearly

 

all the GM products I've owned have had the caliper at the trailing side of the spindle on the front. both indepenent and solid (4X4) suspensions.

vehicles with rear discs have had the caliper at the leading side of the axle. I suspect that is because of the parking brake cable routing.

I once read it had to do with the suspension geometry. I'm sure the engineers must have a good reason.

 

Nope. All the brakes care about is torque, which is purely rotational and doesn't care about the clocking of the caliper. Porsche claims that they put their monster calipers towards the center of the car (forward on the rear wheels and rearward on the front wheels) to minimize the polar moment of inertia for handling. I think that's marketing BS. Unless the calipers are made from lead, the difference is negligible.

New cars have calipers pretty much anywhere from 3:00 to 9:00 on the rotor. The only mechanical reason is to maximize clearance to the shocks and other suspension components.

 

The calliper will normally be place the opposite side of the steering arm, depends on the design of the car.
As Joe said, the callipers don't know where they fitted, they just react to pressure applied to the brake pedal.
Roger.