You make a really good point. My concern for shaving pounds and ounces was probably at its height when I was running marathons and was also quite active in mountain SAR. My pack weight was usually around 45 pounds, occasionally up to 50, and a lot of it was mission critical material whose weight and bulk were fixed -radios, first aid items, climbing gear and the like. Everything that could do double duty, displayed versatility, or that was a bit lighter was welcomed.

The benefit was that I was able to respond immediately with my pack and stay in the field for two to three days, in either the desert or the mountains. There was a lot of seasonal adjustment - one of my colleagues remarked that in the summer our packs became "giant water bottles," and anything but lightweight. There is no getting around the need for water.

Currently, I must admit, I am not in marathoning shape, but I get along reasonably well for an old guy....

Back to your point - at one point, I did work at trimming my weight, getting it down to about 170-175; the improvement in my vigor and endurance was well worth it. Body weight is an excellent starting point for improving performance.

The bottom line is that there is precious little benefit to dragging around a lot of excess weight. Every bit shaved off will enhance performance. And yet, like so many other things, it is possible to carry this process to ridiculous, unproductive extremes.