I have. It will reduce weight, depending on the size of the holes and the depth.

To get a rough idea of the weight saving before you drill, cut some wood dowels the diameter and depth of your holes and weigh them. Walnut will weigh a little more that normal dowels, but this will give you an idea.

Then, it is up to you to decide if it is worthwhile.

As long as the holes are not too close to the edge, nor too deep, I don't think it will weaken the stock. You might consider hollowing out the stock with a Dremel tool. As above, just don't get too close to the edge.