Benefit of shielded ac wire? Any downside?

I have made my own shielded power cords for decades using three conductor 12 gauge cable with a foil shield. I hook the shield up on the house side only. Does it help? I have an extremely quiet system but I can not tell how much the cords add to it. There is certainly no down side as long as you do not hook up both sides of the shield which might produce ground loop hum. There are lots of very sturdy plugs out there. I use Marinco plugs.

As cleeds is suggesting, if the wire is not intended for in wall use do not bury it in a wall. No sane electrician will do this. If the inspector catches it he could lose his license. If you do it and your insurance company catches it (after the fire) you lose everything. If you want to run special wire you can wire it to your breaker box and run it externally. It would be a bit messy but you could do it.
ptss, why do I do it this way? Because it feels good is the best answer. 
There are a lot of wires crossing paths at the equipment rack and I want to shield interconnects from AC as best as possible. Aside from keeping power cables apart from interconnects shielding adds another layer of protection. With the phono stage on and volume opened up to explosion levels all I get is a hiss which you can hear one foot away from the speakers. On the hard drive you can't hear anything even with your head in the speaker. I have not checked this out with the supplied power cables. There may not be any difference but, I've already tossed those.
The Marinco plugs are really nice and they look sharp.