I've always known this, it just didn't hit me real hard until tonight when I did some math.
My bw for lows in the 40's-50's right now is aroung 7.5lbs. I've been seriously considering a few changes (which would cost $$$$) to drop two more pounds off. I would also be sacrificing some comfort to my back. When you look at the math:
2lbs off my baseweight is a 26% weight savings! But...
For a weekend trip where I am hiking all day long, bringing 2lbs of food a day, and carrying an average of 64oz of water (I often hike in very dry climates), my total pack weight with my 7.5lb bw is 16.5lbs. If I drop 2lbs off, that is a 12% weight savings.
For a week long trip, bringing 2lbs of food a day, carrying an average of 64oz water, dropping 2lbs is a 7% weight savings.
In fact, if one of us hit SUB ZERO and went on that weekend trip with me and left EVERY SINGLE OUNCE OF GEAR behind and just brought food and water, they are only 29% lighter.
((( Granted I never ever bring 2 pounds of food a day, but you get the point )))
The other thing to consider is that, yes, the pack will get lighter as your hike goes, and the percent of weight savings will increase (i.e. you will notice the drop in baseweight more significantly by the end of the hike), but the more the weight savings increases, the less you need it. In other words, I needed the weight off my shoulders when it was 25 pounds, not 8 pounds!